~ㄹ 수 없다 VS ~지 못하다 What is the difference between those two ways of saying that one can't do something? Is there a difference or can they be used indistinctly?

What is the correct form of the past tense of the verb 대갑하다 (to answer)? I've just seen this sentence: 선생님이 어제 저에게 대답해 줬어요 = The teacher answered me yesterday. According to the book I'm using, the past tense of 대갑하다 is 대답했어요. That sentence is from that same book, but I don't understand why the correct answer is that one. Shouldn't the sentece above be 대답을 줘어요 instead of 대답해 줬어요? Thank you :)

What is the correct form of this sentence with the verb 듣다? I've just seen this sentence: 조용한 소리를 들을 수가 없어요 = I can't hear quiet sounds. My question is: Shouldn't it be 듣을 instead of 들을? Since the verb is 듣다, why did the ㄷ change to ㄹ? Thanks!

Should I use 에 or 까지 in this sentence? The sentence is: Can you arrive by 12 o'clock? 1. 12 시에 도착할 수 있어요? 2. 12 시까지 도착할 수 있어요? The answer given in my textbook is the second one, but I don't understand why. Since the question refers to an exact time, shouldn't 에 be used? Thanks!

물어보다 and 묻다 What is the difference between 물어보다 and 묻다? Both of them mean "to ask", am I right? I don't really understand the difference. Thanks!

Are this two sentences correct? 저는 크리스마스에 많은 선물을 받을 거예요. 저는 크리스마스에 선물을 많이 받을 거예요. I'll receive a lot of gifts for Christmas. Are both of these sentences correct? I translated it using the first sentence, but I checked the book and the solution is the second one.

Is there any difference between this two sentences? 프랑스는 한국어와 많이 달라요. 프랑스는 한국어와 진짜 달라요. French is very different from Korean. Are the two sentences above correct? Or is the first one more correct?

Is there any difference between this two sentences? 저는 다음 주 화요일에 파리에 가요. 저는 다음 주 화요일에 파리에 갈 거예요. Do the both of them mean the exact same thing? Or does the first one mean "I'm going to Paris" and the second one "I'll go to Paris"? Thanks!

Which sentence is correct? - 책상 위에 과일이 많아요. - 책상 위에 과일이 많이 있어요. There is a lot of fruit on the desk. Which sentence is correct? Or are the both of them correct?