—— The water changes into thick ice covering rivers and lakes in winter in Harbin. —— ____ in Urumqi and children go skating on it then.
--- How long have you been here? --- _____ the end of last month.
We keep in touch ____ writing often.
Who is it up _____ decide whether to go or not?
____ that they are inexperienced, they have done a good job.
Thank you for the trouble you have ____ to help me.