目前对稻飞虱防效最高的药物是（）。
A、毒死蜱
B、叶蝉散
C、燕化扫飞
D、烯啶虫胺
参考答案：C
The teacher tells his students to read the novel over and over again until they ______ it.
A．understand
B．understood
C．have understood
D．have been understood
-56，25，-2，7，4，（）
A．3
B．-12
C．-24
D．5
