Would 13∶00 be convenient—________，but I’ll have to check my schedule for sure

Ladies and gentlemen, please remain _____ until the plane has come to a complete stop [ ]

We the Chinese are not to be ______, ________the situation is. [ ]

Mark isn’t coming to the concert _____ he has finished his work.

When you ______ a difficult task, try to continue with it and finish it.