Storms most commonly occur_______a warm airmass and a cold air mass touch each other.

These problems are too hard to . Will you give me some advice—There are many ways, but the most important is to have a careful plan.

Was the driving pleasant when you went to Mexico last summer? —— No, it ＿＿＿＿ for four days when we arrived, so the roads were very muddy

When ____ to danger and conflict, men tend to increase blood pressure, ____ nervous or anxious.

May I take this book out of the reading room?— No, you ________. You read it in here.[ ]