Generally, words in the English language have numerous antonyms bearing analogous meanings. A buff is a book that contains all these antonyms in one place. 
Let us look at some samples of antonyms. Promote is a word that means fostering the progress of a particular cause laboriously. Nurture can be the another word which can be used to describe this meaning in one word. 
In our question, we've been given the word ‘ litter ’. waste means to throw trash indiscriminately without minding about the consequences. moment, littering is a public nuisance in India. 
Let us consider the given options. 
Option ‘ a ’ dirty means to be covered with sick substances. It's analogous in meaning to waste. thus, it's the correct answer. 
Option ‘ b ’ fill means to beget a space to come full. It's n’t analogous in meaning to waste. thus, it's an incorrect answer. 
Option ‘ c ’ is clean which means to be free from dirt or stains. It's n’t analogous in meaning to waste. thus, it's an incorrect answer. 
Option ‘ d’ is leave which means to go down. It's n’t analogous in meaning to waste. thus, it's an incorrect answer. 
Option ‘ a ’ will be the correct answer.