1. Some students posted a lot of unkind comments, making fun of my pose.

2. Some students posted a lot of unkind comments while they made fun of my pose.

3. Some students posted a lot of unkind comments while they were making fun of my pose.

4. Some students posted a lot of unkind comments, which made fun of my pose.

5. Some students posted a lot of unkind comments, and they made fun of my pose.
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Q1: Which one is smiliar to #1, #2 or #3?
Q2: Do #4 and #5 mean #1? In #4, 'which' refers to 'unkind comments,' right? In #5, does 'they' refer to 'a lot of unkind comments'? Or does 'they' refer to 'Some students'?

3 answers

All the sentences mean about the same thing as #1, yes.

In #4, yes, the antecedent is "comments."

In #5, "they" refers to "students" since both "students" and "they" are the subjects of their own clauses. If "they" were meant to refer to "comments," the word "which" would have been used, as in #4.
Thank you for your help.

4. Some students posted a lot of unkind comments, which made fun of my pose.

5. Some students posted a lot of unkind comments, and they made fun of my pose.

5-2. Some students posted a lot of unkind comments, and they were making fun of my pose.

6. Unkind comments made fun of my pose.

(Can we use Sentence 6? In #4, since 'which' means 'unkind comments,' it seems that we can use #6. Am I right?
Which one is better, to use 'the past tense' or 'to use the past progressive tense'?)
Yes, 4 and 6 have the same meaning, although it seems odd to have the abstract word "comments" be the subject of an action verb "made." It's the people who are making the comments, right?

If the verb's action is in the past and it's over with, then use the simple past.

If the verb's action is in the past and continued for quite a while, then past progressive would be okay.