This could cause serious damage to the country's economy.

　　這可能對國家的經濟造成嚴重破壞。

　　The operation could prolong his life by two or three years.

　　這次手術可使他多活兩三年。

　　Many children can't function effectively in large classes.

　　許多孩子在大班上課時學習效果不好。

　　The results can be divided into three main categories.

　　結果可分為三大類。

　　I could come next week, or the week after.

　　我可能下周來，或者再下一周。