Mashaal Masha
The sun never sets during the Arctic summer in the Far North. In response, reindeer in this region must change their sleep habits. Instead of resting when it gets dark, they rest when they need ________ their food.

Which choice completes the text so that it conforms to the conventions of Standard English?
Difficulty: Easy
A: 

digest

B: 

will digest

C: 

to digest

D: 

digesting