I need a little help on these, i've posted them a few times but i don't get any answers.

29. A common feature of thermal pollution and artificial eutrophication is that they both
a. have sources that are difficult to identify and control
b. cause large mats of algae to bloom in fresh water
c. are a result of power plants and other industrial activity
d. decrease the amount of oxygen dissolved in water

D

33. A true statement about greenhouse gases is that they
a. convert sunlight into eat energy that warms Earth
b. are concentrated in the stratosphere
c. trap hear that is radiated upward from Earth
d. are not affected by human activity

it's either A or C

29. is correct.

Check this site for 33.

http://en.wikipedia.org/wiki/Greenhouse_effect

Right.

To find the correct answers to these questions, we can analyze the given options and apply some basic knowledge.

29. The question asks for a common feature of thermal pollution and artificial eutrophication. To find the answer, let's review the options:
a. have sources that are difficult to identify and control: This option does not directly relate to both thermal pollution and artificial eutrophication.
b. cause large mats of algae to bloom in fresh water: While both thermal pollution and artificial eutrophication can contribute to algal blooms, this is not their common feature.
c. are a result of power plants and other industrial activity: This option is specific to thermal pollution and does not apply to artificial eutrophication.
d. decrease the amount of oxygen dissolved in water: Both thermal pollution and artificial eutrophication can reduce the dissolved oxygen in water, which is crucial for aquatic life to thrive.

Therefore, the correct answer is option d: decrease the amount of oxygen dissolved in water.

33. The question asks for a true statement about greenhouse gases. Let's examine the options:
a. convert sunlight into heat energy that warms Earth: This statement accurately describes the greenhouse effect caused by greenhouse gases.
b. are concentrated in the stratosphere: This option is incorrect because greenhouse gases are generally present in the lower atmosphere, not in the stratosphere.
c. trap heat that is radiated upward from Earth: This statement is also true since greenhouse gases absorb and re-emit heat radiation, preventing it from escaping into space.
d. are not affected by human activity: This option is incorrect because human activities, such as burning fossil fuels and deforestation, contribute to the increase in greenhouse gas concentrations.

Thus, the correct answer is option c: trap heat that is radiated upward from Earth.