I find Physics is so hard for me that sometimes I want to stop learning it.

Can you spare me a few minutes now—______, but I’ll be free this afternoon.

Why did you leave without a word of warning to John—But what _____ otherwise He never listens to me.

Since the war _________ in Syria in 2011, there have been a great many refugees(难民) running to nearby European countries.

____ finding solutions, it isunthinkable to solve all the problems the same way throughout the country.