写出下列词的复数形式。1. a girl 2. a ball 3. an ora

假如你是Mr. liu.阅读下面一封信，请根据信件内容给Tom写一封70词左右的回信。

Dear Mr. Liu:

I failed my math again. I think I’m hard-working and I listen to the teachers carefully in class. I always get nervous while taking an exam. If my mom knows it, she will be mad at me.  What should I do? Could you give me some good advice?

Sincerely,

Tom

Dear Tom:

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Sincerely

Mr Liu

胆碱酯酶复能剂能缓解的有机磷农药中毒症状是（）。

A.肺水肿

B.视力模糊

C.恶心呕吐

D.大汗及流涎

E.全身紧缩感

WD-320稳定车夹钳轮检修时，应进行清洗，更换（）。

A、ZL-2锂基润滑脂

B、HZ-23车轴油

C、N32

D、18#双曲线油

地方性砷中毒常见的临床症状为（）

A.全身皮肤瘙痒

B.皮肤色素缺失或高度沉着

C.恶心、呕吐、全身不适

D.骨质疏松

E.心脏肥大

脂质体的制备方法不包括

A．注入法

B．化学交联固化法

C．超声波分散法

D．逆相蒸发法

E．薄膜分散法