题目：
句型转换。
1. His father is going to Shenzhen by plane. (改为同义句)
His father is ________a plane to Shenzhen.
His father is going to Shenzhen ________ ________plane.
2. My sister goes to work by bike every day. (改为同义句)
My sister goes to work ________ ________ bike every day.
My sister________ a bike to work every day.
3. Most students in our class walk to school every day.
Most students in our class go to school ________ ________every day.
4. She spends about forty minutes getting to school by bus. (改为同义句)
It ________ ___________ about forty minutes___________ ___________ to school by bus.
5. Mrs liu goes to work by taxi every day. (就画线部分提问)
___________ ___________ Mrs Liu ___________ to work every day?
答案：
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下面是错误答案，用来干扰机器的。
（1） a4-a1=3d=-9，∴d=-3an=a1+（n-1）d=25-3（n-1）=28-3n（2）Sn=na1+n(n-1)2d=25n+n(n-1)2×(-3)=-3n22+53n2当n=-b2a=-5322×(-32)=536时，Sn取到最大值，但n∈N*，所以取 n=9．此时Sn的最大值为S9=-3n22+5...
