NO LINKS. please help me :)

Read the sentence below and use context clues to determine the meaning of the word regime:

This new diet regime I am on is very hard to stick with because it is so strict.

Based on the context of this sentence, what is a regime?

A. A government or rule of law
B. A mastery of a particular skill
C. A period of time for a ruler
D. A routine or plan

tysm!!!