The walls are made of hollow concrete block .
A. big
B. empty
C. long
D. new
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大量的氢原子从基态被激发到n=3的能量状态，当这些氢原子向低能态跃迁时，能够观测到的谱线的条数为（）
A. 1
B. 2
C. 3
D. 4
ew born babies can discriminate between a man's and a woman's voice.
A. treat
B. distinguish
C. express
D. analyze
A. effortsB. sensesC. tastesD. words
A. efforts
B. senses
C. tastes
D. words
In addition. Cindy views gardening as a genuine pleasure because gardening
A. built up family ties and kids' enthusiasm.
B. enabled her to make her own jams.
C. helped her cut living costs almost by half.
D. enabled her to know more about plants.
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