It was playing computer games that _______ the boy plenty of time that he ________ doing his lessons

题干

It was playing computer games that _______ the boy plenty of time that he ________ doing
his lessons.

A：spent; must have bee

B：cost; ought to have spent

C：wasted; wouldn’t have bee

D：took; can’t have spent

上一题下一题 0.0难度选择题更新时间:2019-12-24 04:46:35

B

太阳能热水器是直接利用太阳能给水加热的装置，下表是小明家的太阳能热水器某天在阳光照射下的相关信息

太阳照射时间/h	装水量/kg	吸热板面积/m²	水升高的温度/℃	水的比热容/J（kg•℃）^﹣1	太阳辐射功率/J•（m²•h）^﹣1
10	100	2.5	50	4.2×10³	1.68×10⁶

其中太阳辐射功率是指1h内投射到1m²面积上的太阳能．
求：（1）水在10h内吸收的热量；
（2）如果水吸收的热量用天然气来提供，需要完全燃烧多少m³的天然气；（天然气的热值为8.4×10⁷J/m³，天然气完全燃烧放出的热量全部给水吸收）
（3）该太阳能热水器的能量转化效率．