题目

I break off a piece of candy and take pleasure in its sweet outside and the bitter, dark chocolate inside, thinking of my own life. Being raised by a single parent was a bitter-sweet 36 , which gave me motivation and ambition. There were several years that have left a(n)  37   bitter taste in my mouth —those when my mother married a man and moved my sister, Emily, and me several states away from our hometown. The first few months were  38  : baseball games, family trips to the mall, dinners and movies together. Then things changed. Baseball became too expensive, and trips to th小稳家需要将50kg、200℃的水加热到600℃作为生活用热水，她们利用煤气灶烧水，需燃烧0.8m3煤气．已知煤气的热值q=4.2×l07J/m3，水的比热容C水=4.2×l03J/（kg℃）．求：（1）50kg、20℃的水加热到60℃需吸收的热量．（2）完全燃烧0.8m3煤气放出的热量．（3）煤气灶烧水的效率．