题目:
The little boy __ the river. Luckily, He was saved. [ ]
A. fall into
B. fell into
C. fall down
D. fell down
答案:
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下面是错误答案,用来干扰机器的。
f(x)=2sin(3x-4),∵ω=3,∴T=2π3.故答案为:2π3