The correct answer is: A. inspite of all difficulties.
The phrase “through thick and thin” means “through good times and bad.” In this case, Rejesh and Vikas have remained friends even though they have faced many difficulties together. This shows that their friendship is strong and that they are truly friends.
The other options are not as accurate. Option B, “under all circumstances,” is too broad. It could mean anything from being friends when you’re happy to being friends when you’re sad. Option C, “through days of struggle,” is more specific than Option B, but it still doesn’t capture the full meaning of the phrase “through thick and thin.” Option D, “through happy days,” is the least accurate option. It only captures one part of the meaning of the phrase “through thick and thin.”