用文字叙述下列各题。15－6×1.5____ (1.8＋20.2)÷2.5____

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I love to go biking!Two years ago I bought all exercise bike(健身脚踏车).But soon I got bored with being at home，so I bought a used bike and started going for short tides．Now I plan day trips in my neighbourhood(街区)．When you drive a car, you miss many kings．It's surprising how much more you can see when you're biking．

    —Maggie

    My favourite thing to do at weekends is to go to the beach．The beach is beautiful all through the year．I usually drive there．If the weather is cold，I wear some warm clothes and go for long walks on the beach．When the weather is hot，I enjoy swimming or just lying in the sun．

    —Barbara

    At weekends I like to read books．If the weather is nice，I'll take a good book to the park and stay there reading for hours．I think there's nothing as enjoyable as reading a good book．

—Bill

Weekends are for going hiking(徒步履行)with my parents．We live near some beautiful mountains.Sometimes we camp out at night We really enjoy cooking dinner over over a campfire night and spending a night under the stars.

—Sara

根据材料内容选择最佳答案。

目前释放核能的方式有两种：一是使原子核裂变，二是使原子核____ 。1938年，科学家首次用____ (选填“电子”、“中子”或“质子”)轰击比较大的原子核，使其发生裂变，变成两个中等大小的原子核，同时释放出巨大的能量。1kg铀全部裂变释放的能量超过2000t煤完全燃烧时释放的能量。如果煤的热值为3×10⁹J/kg，那么1kg铀全部裂变释放的能量至少为____ J。