[TOMT] Scifi and Fantasy books I read as a child about 15 years ago [books]

Edit: ** Everything but number 1 is found**. Thanks a lot to those who have helped :D , now I know what to read on my trip. This subreddit is awesome.

I read some sci-fi books as child and since all of them were English to Farsi translations kI have no idea about their titles nor do I have any useful keywords I can use to search for them. I'm really curious to re-read some of these books in English now. Specially the first one.

1- Book about an earthian who had lost his memory and was found wandering around in a garden in another planet/asteroid with residents of lower social status . I think men were not allowed to look at women of higher status and this gave away the protagonist's friend at some point when they tried to blend in with another population. At the end it was revealed that the protagonist knew of an eminent danger approaching earth and a colleague in order to calm him down tried to erase his stress with a brainwashing device but since the protagonist was nothing but stress it caused him to lose his memories completely.

2- A short story about residents of an asteroid who take a lot of pride in their artificial food and shun natural food. The protagonist travels to earth for a year and is ridiculed for eating dirt when he gets back. He later competes in a food testing contest, wins a perfect score from the judges and then reveals that he had used garlic in his formula which cause the judge to vomit in disgust. ** Good taste by Isaac Asimov**

3- Two boys (or maybe adult men) get stuck in a cave on moon which is filled with breathable air, they discover a sentient plant inside and a long lost astronaut who had been thought to be dead. I remember the plant didn't allow them to leave the cave and tried to slowly make them part of the ecosystem like the previous astronaut. Lotus Caves by John Christopher

4- In a double star system scientists separately figure out that every few thousand years an objects blocks out both of the suns which causes the inhabitants to go insane from darkness and burn down their civilization. Nightfall by Isacc Asimov

There is more, but this post is long enough already. I'd really appreciate any hints.