Can you tell me ________ the train was invented

Some people complain that it usuallyso long to buy train tickets during the Spring Festival

I am not sure whether I will have anything else to do tomorrow _____, I will try every possible means to come to the party[ ]

_____ by it’s impressive performance, Peter will probably be accepted by a key university. [ ]

I can’t say ______I want to see him again. We haven’t seen each other for a long time.