[单选题]Science is still ______ of the causes of many kinds of cancer.

正确答案 ：A

ignorant

解析：解析：ignorant可以指“无学识的，愚昧的”，还指“不知道的”；unconscious意为“失去知觉的，不省人事的；无意识的”；conscious意为“有知觉的，意识到的”；informed意为“获悉，告知”。

[单选题]According to the passage, the first settlers used wood for their utensils and tools because it was ______.

正确答案 ：C

available

解析：解析：注意题干上的信号词utensils and tools，以此为目标可以很容易地找到本题的依据句“Because of the lack of other materials，early settlers were forced to make tools and utensils out of wood.”选择C的原因在于当时十分缺乏其他材料而木材到处都有所以得到采用。available意思为“有，存在”。

[单选题]All the firemen in the city were ______to fight against the big fire.

正确答案 ：C

called up

解析：解析：called in意为“回收”；called off意为“取消”；called up 意为“召集，打电话，使人想起”；called on意为“访问(某人)”。

[单选题]Tom: You are playing guitar well. Can you read music? Charles: No, I don't. I just listen to songs on the radio and then play them until they sound right. Tom: ______ Charles: No, really.

正确答案 ：D

You're kidding

解析：解析：Tom对Charles不识乐谱也能弹得一手好吉他感到难以置信，这种情况下一般说 You're kidding或You're joking，意思是：“你在开玩笑吧!”或“这不是真的!”。其他几个选项分别表示“撒谎”、“吹嘘”、“欺骗”，都不恰当。

[单选题]Guest: Oh, I hadn't realized how late it was. I'm afraid I'll have to be going. Host: Oh, not yet. I'm just going to make some coffee. Guest: ______ , though I'd really love to stay. I've got to be up by six tomorrow morning, unfortunately. Thank you for a wonderful party.

正确答案 ：A

I'm sorry, but I must

解析：解析：主人诚心挽留，客人坚持要走。由于不能接受主人的好意，客人应表示歉意，故而选择A．I'm sorry，but I must比较合理。其他选项使用场合不当。

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