短文改错。
There have be a lot of changes since World 1._____
WarⅡ. But perhaps a biggest change is 2._____
the telephone. People no longer write
letters for one another. They pick up the 3._____
telephone. Every house has at least two,
sometimes three, four and five telephones. 4._____
Every office has many telephones. There
have more telephones than people in 5._____
American. My little house has three 6._____
phones. In the morning the first thing
which wakes me is my telephone ring. 7._____
Long distance telephone call are very 8._____
cheap before seven o'clock in the morning.
So that my friend in Boston telephones me 9._____
to say “Good morning.” If you never have
to write a letter, you simple take up the 10._____
telephone and say what you want to say.
沿x轴正向传播，坐标原点的振动表达式为y0=6×10-2cos
，则当t=5s时该波的波形曲线方程为（）。
