问题
选择题
| This is the first time that I _____ at the meeting. |
A. had spoken B. have spoken C. spoken D. speaking |
答案
答案：B
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| This is the first time that I _____ at the meeting. |
A. had spoken B. have spoken C. spoken D. speaking |
答案：B
则关于t的一元二次方程9t2+4Xt+1=0无实根的概率等于（）．