衡量疾病危险程度的指标是
A．患病率B．感染率C．引入率D．发病率E．续发率
参考答案：D
The thought of going back home was ____ kept him happy while he was working abroad. [ ]
A. that
B. all that
C. all what
D. which
下列哪一类氨基酸只含非必需氨基酸（）。
A.碱性氨基酸
B.酸性氨基酸
C.分支氨基酸
D.芳香族氨基酸
E.含S氨基酸
