小船在静水中速度为v，今小船要渡过一条河，渡河时小船上的人朝对岸垂直划行，若划行至河中心，水流速度突然增大，则（ ）
A．渡河时间增大，渡河位移也增大
B．渡河时间增大，渡河位移不变
C．渡河时间不变，渡河位移变大
D．渡河时间不变，渡河位移不变
答案：C
根据各分运动具有独立性，水流速发生变化不会影响渡河时间，水流速度增大后沿河向下游的位移增大，渡河位移增大，C对；
| 选择方框内恰当的单词并用其适当形式将短文补充完整. | |
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| My father is very busy. He usually works five __1__ a week from Monday to Friday. __2__ he works on Saturdays _ 3__ Sundays. He often gets up early in the morning. He cooks __4__ for my family. He goes to work at 7:10. He __5__ lunch at his workplace. He comes back _ 6__ at about 6:30. My mother cooks dinner. _ 7 _ dinner he goes out and takes a __8__ in the small garden. _ 9 _ he goes to bed, he often reads some _ 10 _ or watches TV. He goes to sleep very late |
