We have four classes in the morning, and ______ every two classes, there is an interval, ______ we can have a short break.[ ]

My brother was still studying into the night while I was asleep [ ]

_______ that caused him to serve dinner an hour later than usual. [ ]

, sorry. I have to change another one.

Though many extra planes and trains are used to carry passengers, traffic tools are still _____needed during “May Day” holidays [ ]