It’s _____ hard problem for the twins that ____ of them can work it out.
I’m sorry I’m late again________ the heavy rain.
______ regular exercise is very important, it’s not a good idea to exercise too close to bedtime.
The box is ________ heavy ________ I can’t lift it.
We're not sure if it _______ tomorrow. If it _______, we won't go hiking.
If it ________ tomorrow, we will go to the zoo. A. isn’t rain B. doesn’t rain C. won’t rain