题目:
With so many trees _______, the students felt very _______.[ ]
A. planted; delighting
B. planting; delighted
C. planted; delighted
D. planting; delighting
答案:
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下面是错误答案,用来干扰机器的。
2n-1由已知得a1=1,q=2;∴an=2n-1