题目内容

【题目】铁生锈的条件是_____________并存,铁锈的主要成分是_________,铁锈是一种混合物,铁生就后变得疏松多孔,因而不能阻止铁继续被锈蚀,破坏铁生锈的条件就能防止铁生锈。

【答案】水和空气;氧化铁

【解析】铁生锈是铁在空气中与氧气和水发生的缓慢氧化的过程,该变化需要氧气和水同时存在,缺一不可;铁锈是一种混合物,其主要成分是氧化铁。

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【题目】B

What do we do when we go camping? First, we think of a plan. We take food, clothes, a knife, and things for cooking and eating. We take things to keep us away from insects(昆虫) and the sun. Then we put everything into the car and we drive to the woods. We look for a place for campers(露营者) and we look for a good place for our tent(帐篷). The place should have a lot of air. This will keep some insects away. High land with water on both sides of it is good. Then we put up our tent. We put everything into the tent, and we are ready for fun. We can swim in the lake, walk in the woods, climb a mountain, row a boat, or go fishing. In the evening we come back to the tent, we build a big fire because it can keep the insects away. We sit around the fire and talk. We may tell interesting stories or we may sing songs. At night we lie down on the grass. We can look up at the stars. It is a busy day, so we try to go to sleep early. Everything is dark. Everything is quiet. We hope we won’t hear music from the radio in the next tent. We hope it won’t rain.

【1】Before going to camp we should first __________.

A. think of a plan B. take some food

C. take things to keep us warm D. take something for cooking and eating

【2】 We go to camp __________.

A. by bus B. bycar C. by bike D. on foot

【3】Campers can join in __________ activities.

A. one or two B. only a few

C. many D. two or three

【4】In the evening we build a fire because __________.

A. it is cold at night B. it can keep us warm

C. it can keep the insects away D. it is dark and quiet

【5】The campers like to __________ at night.

A. hear music from the radio B. go to sleep early

C. have rain D. be busy

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