It’s really difficult to what he is trying to express.
A. leave out
B. pick out
C. work out
D. make out
网友回答
A. leave out
B. pick out
C. work out
(答案→)D. make out
解析：A. leave out遗漏，B. pick out 挑选出，辨认，C. work out制定出，锻炼，D. make out辨认，理解，句意：真的很难理解他想表达什么。所以选D。