Read the sentence and decide which answer A, B, C or D best fits the space and completes the idiom. Harry couldn't stand his superiors... and stick approach, so he quit his job.…

The best answer to complete the idiom in the sentence is:

a. carrot

The complete idiom is "carrot and stick," which refers to a policy of offering a combination of rewards and punishments to induce desired behavior. So the sentence would read: "Harry couldn't stand his superiors' carrot and stick approach, so he quit his job."