The correct answer is A. Much ... effect
Explanation
To ask questions in English you can use "how much" and "how many"; these two differ in that the first is used to ask for uncountable nouns such as air, salt, sugar, among others, while the second is used for countable such as apples, people, animals, hours, among others. Therefore, the most appropriate word to ask about the amount of salt that is healthy to eat per day is "how much". On the other hand, the word "affect" is a verb that refers to action, while "effect" is a noun that refers to the consequences of an event. So, the most appropriate is the noun because the text is wondering about the effect that salt has on health and not how it "affects" health. So the answer is A. Much ... effect.
D, I believe, since the others do not make sense if you read them.
Here are the answers for the exercise
1. have been
2. did she meet
3. has he been
4. went
5. have we owned
6. did she graduate
7. did the children go
8. didn't write
9. drank
10. Has she ever tried
11. have you lived
12. Have you ever been
13. didn't go
14. did you go
15. Have you eaten/ Did you eat (Both is correct)
16. have wanted
17. has had
18. didn't see
19. did you have
20. Has he ever played
