At least some students are in the habit of doing their exercises in a slovenly manner.

The correct answer is A. neat.

The word “slovenly” means “careless or untidy in appearance or habits.” So, the answer must be a word that describes someone who is careful and tidy. Of the four options, only “neat” describes someone who is careful and tidy.

“Proper” means “correct or appropriate.” “Decent” means “morally good or respectable.” “Correct” means “free from error.” None of these words describe someone who is careful and tidy.