单项选择题A.It has been increasing since the Ice Age.B.It affected the growth of trees.C.It is determinated by the chemicals in the air.D.It follows a certain cycle.
单项选择题A.The assignment looks easy but actually it’s quite difficult.B.They have plenty of time to work on the assignment.C.The assignment is too difficult for them to complete on time.D.They cannot finish the assignment until Thursday.