Pick out the most effective word from the given words to fill in the blank in each sentence to make the sentence meaningfully complete.
They work hard not because of the __ , but because of their inner urge.
Inner urge is same as internal motivation. Hence motivation can be ruled out. The use of 'but' implies that the word in the blank should be contrasting to inner urge. Hence 'desire' is correct for the given blank. So the correct answer is option A