根据下列句子及所给首字母，写出单词的适当形式，每空一词。

小题1:We have three m________ a day. They are breakfast, lunch and supper.

小题2:They took quite a f_______ photos in Guizhou.

小题3:I d_______ playing computer games. I think they are boring.

小题4:I exercise t________ a week, every Wednesday and Friday.

小题5:It is sunny today, so it is not n_________ for you to take an umbrella.

有些材料在温度很低的情况下电阻为零，这种材料叫超导材料．假如科学家在常温下研制出这种材料，那么它合适制作（　　）

A．白炽灯的灯丝

B．加热器的电热丝

C．熔断器的熔丝

D．输电线的导线