若要生成40g氧化镁，则至少需要镁条的质量为（） A．24g _爱下问搜题

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问题选择题

若要生成40g氧化镁，则至少需要镁条的质量为（　　）

A．24 g

B．8 g

C．32 g

D．36 g

答案

设参加反应的镁的质量为x

2Mg+O₂

点燃

.

2MgO

48 80

x 40g

48

x

=

80

40g

x=24g

故选A

选择题

—Does Liu Hui serve in the army?

—No, but he ________ in the army for three years.

A．served

B．has served

C．is serving

D．would serve

选择题

_____these interruptions,the meeting

would have finished earlier.

A．Except for

B．But for

C．Apart from

D．Other than