He promised to do what he sure of .
A. could make; my happy
B. could to make; me happy
C. could make; my happiness
D. could to make; my happiness
网友回答
A. could make; my happy
B. could to make; me happy
C. could make; my happiness
(答案→)D. could to make; my happiness
解析：
本题句意“他许诺做他能做的保证使我幸福”。what he could (do)to make sure of my happiness，其中to make sure of my happiness做状语。