There is a d________ between the two pictures. You will find it if you are careful enough.
In the north of China, leaves usually fall when a ________ comes.
The winter is coming. My mother sends me a hat and a pair of g________.
(2018广州)Please open the w________ and let some fresh air in.
I still remember my first teacher________we haven't seen each other for many years.
A.for B.because C.since D.though
The rivers will become dirtier and dirtier ________ we take actions to protect them.
A.since B.if C.until D.unless
