单项选择题

Questions 7 to 10 are based on the following conversation. At the end of the conversation, you will be given 20 seconds to answer the questions.
Which of the following is INCORRECT about the mobile according to the conversation

A.It is made of pieces of aluminum.
B.It can move slowly in the air.
C.It was originally made of steel.
D.It is not safe because of its weight.