对于哺乳动物来说下列哪一种氨基酸不是必要氨基酸（）.
A.Lys
B.Phe
C.Leu
D.Tyr
参考答案：C
There are altogether eleven books on the shelf,_________ five are mine. [ ]
A. on which
B. in which
C. of which
D. from which
要在工具箱中选取工具按钮，（）说法错误的。
A、用每个工具的便捷键
B、直接用鼠标点击工具
C、双击在打开的菜单中选择工具即可
D、直接选择菜单
