You can ship the queue if you have a ticket.
You have to stay if you don't' have a ticket .(have) 这句话我不是很确定,我理解为如果你有票的话可以排队前进.不知道是否正确.
You should go if you are busy
You do not have to stay behind if you are busy.(have)
I need to ask for a doctor's certificate.
Must not forget to get a doctor's certificate.(must)
Is taking photos inside the gallery prohibited?
Are we allowed taking photos inside the gallery?(allowed