下列哪种氨基酸是半必需氨基酸()
A.苏氨酸
B.脯氨酸
C.酪氨酸
D.赖氨酸
E.亮氨酸
参考答案:C
______ close the door. [ ]
A. don't
B. Don't
C. Doesn't
D. Aren't