The primary reason that the existence of Social Security greatly lessens the demand for other forms of social welfare is that

a. Social Security is so popular that many people believe other welfare programs are neither necessary nor desirable. WRONG

b. the anticipation of Social Security benefits upon retirement leads many people who need public assistance to believe there is a better life ahead if they will only wait for it. WEIRD AND WRONG

c. Social Security checks keep millions of elderly Americans with no other source of income out of poverty. COULD BE POSSIBLE

d. the incentive of Social Security benefits upon retirement encourages individuals to work during their productive years, which reduces the need for other forms of social welfare, such as unemployment benefits. COULD BE

e. None of these answers is correct. HMM

Please check

Of these four choices, C is probably best.

I am sort of new to this whole American system and welfare, but social security is basically a different a future trust fund type thing right?

Yes, in a way.

A worker and his/her employer pays into SS (also called FICA), each paycheck, and if it's paid into for at least 40 quarters (ten years), then the worker is eligible for some level of supplementary retirement income after reaching a certain age.
http://www.google.com/search?rlz=1C1GGGE_enUS379US379&gcx=w&sourceid=chrome&ie=UTF-8&q=fica

It was never intended to be a person's entire retirement income. It was intended to be supplemental, but unfortunately today, there are many retired people for whom this is their only income.

That is probably because they completely rely on it now eh?

Does everyone get a chance to fill Social Security ?

Only those who have paid into the system for at least 40 quarters. In some places, there are large cadres of workers who have never paid into SS. One example is teachers in California classrooms (and 13 other states, too, I've read). They pay into the State Teachers Retirement System (CalSTRS), but not into SS. Therefore, anyone who teaches in California classrooms for their entire career cannot apply for SS. (If any have worked at other jobs and/or in other states where teachers DO pay into SS, they might qualify for SS.)

To determine the correct answer, let's examine each option:

a. Social Security is so popular that many people believe other welfare programs are neither necessary nor desirable.
This statement presents an assumption but does not necessarily explain why the existence of Social Security lessens the demand for other forms of social welfare. Therefore, it is not the correct answer.

b. The anticipation of Social Security benefits upon retirement leads many people who need public assistance to believe there is a better life ahead if they will only wait for it.
This option suggests that people who need public assistance may choose to rely solely on Social Security benefits, thus reducing their demand for other forms of social welfare. However, this is not a direct explanation and may not be applicable to everyone. Therefore, it is not the correct answer.

c. Social Security checks keep millions of elderly Americans with no other source of income out of poverty.
This option directly explains how Social Security benefits, by providing income to elderly individuals without alternative sources of income, reduce the demand for other forms of social welfare. This could be a possible correct answer.

d. The incentive of Social Security benefits upon retirement encourages individuals to work during their productive years, which reduces the need for other forms of social welfare, such as unemployment benefits.
This option suggests that the existence of Social Security benefits incentivizes individuals to work and be self-sufficient, ultimately reducing the need for other forms of social welfare. This could also be a possible correct answer.

e. None of these answers is correct.
This option states that none of the previous options provided is the correct answer. However, as we have identified two potentially valid answers, this option is not correct.

Based on the analysis, options c and d could both be correct explanations for why the existence of Social Security lessens the demand for other forms of social welfare.