In 1 you could also say "the snake". In 2, it's true that "fruit" is singular, but that is because it's uncountable. There's no problem in making the answer plural (if that was your doubt).
In a test where you have to choose the grammatically correct answer, it is right to see if the article is used correctly: snake or a snake. In a vocabulary test, where you have to choose between snake, goose and tiger, for example, the use of the article is
By "choosing the grammatically correct answer" I mean that from the possible answers given it is clear whether your grammar or your vocabulary is being tested. In the second case the grammatical form is probably not so important but, as I said before, it is still preferable to give something that can be inserted to give a grammatically correct sentence.