Answer:
Sentence 3 - D (verb is already in the present tense - no change needed)
Sentence 8 - C ( change past to present tense )
Explanation:
Independent clause. because they are going to do it.
A complex sentence contains one independent clause and at least one dependent clause. Here, in your example, there are two simple independent clauses which you need to merge using a dependent adjectival clause in order to make one complex sentence. Here is how to do it:
The boy <u>who wore a green coat</u><u /> carried his sister home.