Today is Tree- Planting Day. I go to the park with my parents. At about ten o'clock we start to plant trees. We needn't to dig holes because the people in the park dug them before. We just put the young trees into the holes. My father fills the holes with me. My mother carries water for the young trees. We are so tired when we finish the work. All of us hope the trees will grow well. I hope I can plant trees next year.

下列几种估测中，最符合实际情况的是（　　）

已知双曲线 $\frac{x^2}{25}-\frac{y^2}{9}=1$ 的左支上一点M到右焦点F₂的距离为18，N是线段MF₂的中点，O是坐标原点，则|ON|等于（   ）

下面句中有一处错误，请找出来并改正。

—Do your friends play basketball? 

—Yes, they play.

____