Teacher: Why are you so late?
Student:______________
(A) I did not woke up on time.
(B) I didn't awake up on time.
(C) I didn't wake up on time.
(D) I not wake up on time.
21 By this way biofuels help fight global ______by producing fewer greenhouse gases than gasoline fuels.
(A) warning (B) warming (C) air-conditioning (D) cooling