We are faced with the problem _________ we should do with so much pollution.
Cars do cause us some health problems——in fact far more serious ______ than mobile phones do.
–If you like I can do some shopping for you.–That’s a very kind _______ .
I could have offered you some help last weekend, but I _______ with my work at that time.
__________ he sees people in trouble, he always lends them a hand.
She has been working hard day and night, which of course, _______ her pale face.