Hey Haewon!
#6:
This question is a little tricky because (like you thought) if you understand the topic too broadly, you might think the two sentences are continuing ideas. However, if you read more closely, the topic is differing ideas because the first sentence is about where MOST of the movie was shot, while the second sentence is about where the LAST scenes were shot, which are differing ideas. If the second sentence CONTINUED THE DISCUSSION filming most of the scenes, then a continuer, such as additionally or moreover would work. Also, keep in mind that if you have TWO answers that have the same function (additionally, moreover, furthermore, also, besides), both answers can't be correct. =)
#3:
Same exact reason as #6. =)
Sometimes, if you think about the sentences too broadly, you might get confused. The first sentence is about MOST of the poems, while the LAST poem is the topic of the second sentence, which requires a contrasting transition. Transitions like ADDITIONALLY, MOREOVER, FURTHERMORE, ALSO, BESIDES, WHAT'S MORE, IN ADDITION are all synonyms. They are used to CONTINUE THE DISCUSSION of the topic of the first sentence.
Example:
Jack was convicted of armed robbery. Furthermore, he was charged with assault. The second sentence continues the discussion of the first sentence (the crimes Jack was convicted of).
You will get better with more practice over time. =) Stick with it. I've attached other transition problems for you to practice, too. =) Also, a good tip is that if TWO answers have transitions that have the same function, BOTH of those answers are wrong.
You got this, Haewon!