Hello and thank you sincerely in advance for your help. I'm an aspiring English teacher trying to familiarize myself with all the nuances of the language :)

I am trying to identify which word in the following 6 questions are used incorrectly, explain why they are used incorrectly as well as replace the incorrect word with a better alternative. So far, I have identified (what I think) are the incorrect words and replaced them with (what I think) are the better alternatives. However, I'm really not sure how to explain the decisions that I've made.

If you would be so kind, please look at the following 6 questions and help me Identify and explain the correct choices.

A. In the sentences below, one of the words is used in a way that sounds strange or inappropriate.

Identify the wrong word then supply a more appropriate word and say why this is better.

A healthy diet makes people skinnier and better looking.

ANSWER: ‘Skinnier’ is wrong here. ‘Slimmer’ is better because it has a positive tone. ‘Skinnier’ sounds too negative in this context.

1. The students have done a lot of progress so far.
Answer: ‘done’ is wrong here. ‘Made’ is better.

2. He doesn’t concentrate in class, he spends most of his time saying jokes to his friends.
Answer: ‘Saying’ is wrong here. ‘Cracking’ is better

3. The assistant manager left last week so now we’re trying to find out a replacement.
Answer: ‘Out’ is wrong here. It should be deleted because it is extraneous.

4. The work I’m doing at the moment is absolutely difficult for most people.
Answer: ‘Absolutely’ is wrong here. ‘Very’ is better.

5. Please could you cough up this money within the next seven days?
Answer: ‘Cough up’ is wrong here. ‘Come up with’ is better.

6. If things aren’t going well it’s important to keep going and not lose bravery.
Answer: ‘Bravery’ is wrong here. ‘Courage’ is better.

Thank you again,