问题
选择题
原子核X衰变为原子核Y，再衰变为原子核Z的过程为：
，下述各关系中正确的是
A．
B．
C．
D．
答案
答案：B
原子核发生β衰变时，质量数不变，电荷数加1，所以a=c，b=d-1，原子核发生α衰变时，质量数少4，电荷数少2，所以c=e-4，d=f+2，综合也有a=e-4，
，故只有B正确
故选B
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原子核X衰变为原子核Y，再衰变为原子核Z的过程为：，下述各关系中正确的是
A．
B．
C．
D．
答案：B
原子核发生β衰变时，质量数不变，电荷数加1，所以a=c，b=d-1，原子核发生α衰变时，质量数少4，电荷数少2，所以c=e-4，d=f+2，综合也有a=e-4，，故只有B正确
故选B
完形填空：（满分20分） Far from a Family Christmas My Air Force room in Florida was 36 and quiet—I was alone．My five roommates were gone for the holidays; I had chosen to 37 behind in the camp．Being young and far from my home, I felt 38 ．My room was comfortable enough, 39 I hadn’t realized until then what made it so—the 40 of others walking, joking or just lying on their beds． I was not able to sleep．I was 41 of being on my own—in fact, preferred it at times—but tonight was 42 ．Tossing and turning in the darkened room gave no 43 ．The last sign of daylight had disappeared, 44 my inner depression． 45 , the glow of Christmas lights on the tall pines would only 46 me of my great misery. Suddenly, I heard weak sound of men 47 to sing．Yes, the voices grew louder and came my way．I 48 still, enjoying the sound. In the corridor(通道，走廊) 49 my room, voices came near enough for me to hear Christmas carols（颂歌） being 50 ．Suddenly, there, four airmen, identities unknown, were slightly unsteadied by holiday 51 ．The first held a Coke bottle with a lit candle 52 its top．The others formed a dancing line behind him. 53 I was in the room, with joyful faces in the flickering(摇曳的) light, they sang me several carols, wished me a 54 and left as fast as they had arrived. I slept soundly soon after, burying my face in my pillow, 55 that someone had cared.
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