听一段材料，回答下面几个小题。What are they talking about?
A.A story about a friend who was on a sweet potato diet.
B.How to keep diet.
C.People should eat all kinds of things.Why was the friend ill?
A.Because he wanted to lose weight.
B.Because sweet potatoes can’t provide him with everything he needs.
C.Because he ate sweet potatoes.What is the best way to keep diet?
A.To eat every kind of food.
B.To eat less meat.
C.To eat less and exercise more.
听一段材料，回答下面几个小题。What are the two speakers talking about?
A.Thunder and sound.
B.Thunder and lightning.
C.Thunder and science.Why is the man unlikely to see lightning?
A.He is asleep.
B.He is reading a science book.
C.Perhaps lightning is far away.
Who are the two speakers?
A.Retired soldiers.
B.College students.
C.Army people.
What happened to the speakers?
A.They lost their way.
B.They were caught in the traffic.
C.They broke the traffic rule.
What is the weather usually like in May?
A.Warmer and drier.
B.Cooler and drier.
C.Warmer and damper.
How many letters does the man write to his mother in a month?
A.Eight.
B.Four.
C.Twelve.