The trip led to an argument between Helen and ? a. I. b. me. (A)

It was ? who demanded an apology from the newspaper. a.we b.us (B)
We appreciated ? writing a personal letter to explain his stand on the issue. a.his b.him (B)
The most outspoken critics were my sister and ? a.I. b.me. (A)

Please list just your answers for each one.

1. he trip led to an argument between Helen and ? a.I b.me (A)

2. It was ? who demanded an apology from the newspaper. a.we b.us (B)
3. We appreciated ? writing a personal letter to explain his stand on the issue. a.his b.him (B)
4. The most outspoken critics were my sister and ? a.I b.me (A)

1. No

2. No
3. No
4. Yes

Study these:
http://grammar.ccc.commnet.edu/grammar/cases.htm (Scroll down a bit and notice in the chart which pronouns can correctly be used as subjects and which as objects.)
and
http://grammar.ccc.commnet.edu/grammar/gerunds.htm#possessive

To determine the correct answers, we need to identify the pronouns that correspond with the subjects of the sentences.

(A) The trip led to an argument between Helen and ?
To find the correct pronoun, we need to know whether Helen is the subject or the object of the verb "led." If Helen is the subject, the correct pronoun will be "I." If Helen is the object, the correct pronoun will be "me." In this case, since Helen is involved in the argument and not leading it, the correct pronoun is "me." Therefore, the correct answer is (A) me.

(B) It was ? who demanded an apology from the newspaper.
Again, we need to determine whether the unknown pronoun corresponds with the subject or the object of the verb "demanded." If the unknown pronoun is the subject, the correct pronoun will be "we." If the unknown pronoun is the object, the correct pronoun will be "us." In this case, since the unknown pronoun is the one demanding the apology, the correct pronoun is "us." Therefore, the correct answer is (B) us.

(B) We appreciated ? writing a personal letter to explain his stand on the issue.
For this question, we need to identify whether the unknown pronoun refers to the person who wrote the personal letter (the subject) or to the personal letter itself (the object). If the unknown pronoun refers to the person, the correct pronoun will be "his." If the unknown pronoun refers to the letter, the correct pronoun will be "him." In this case, since we are referring to the person who wrote the letter, the correct pronoun is "him." Therefore, the correct answer is (B) him.

(A) The most outspoken critics were my sister and ?
To determine the correct pronoun, we need to know if the unknown person is the subject or the object of the verb "were." If the unknown person is the subject, the correct pronoun will be "I." If the unknown person is the object, the correct pronoun will be "me." In this case, since the unknown person is also a critic, the correct pronoun is "I." Therefore, the correct answer is (A) I.