Cycling is a very useful way, especially in cities _______ bike paths have been built

填入下面一段文字横线处的语句，最恰当的一句是 （ ）血栓闭塞性脉管炎又称“脉管炎”，虽是一种血管的炎症，但并不是细菌感染引起的的，而是血栓阻塞血管、血流减少所致，主要以下肢为主。脉管炎后期可引起手足发黑、坏死。但 ，如果在早期能明确诊断，及时治疗，可以避免发生严重的后果。

Some students are seriously ill and they can’t class for several days. [ ]

The pear tree is .We can pick pears easily.

Would you mind ____ the window -Of course not.I feel hot,too.