我国现行的《城市区域环境噪声标准》(GB 3096—93)规定了城市( )类区域的环境噪声最高限值。
A．3
B．4
C．5
D．6
参考答案：C
Students are warned ________ in the exam, otherwise they will be severely punished.
A．to not cheat
B．not cheating
C．not be cheated
D．not to cheat
嘌呤核苷酸从头合成途径中先合成的前体是
A．AMPB．UMPC．IMPD．GMP
