以下哪一项不是预防计算机病毒的措施？（）
A.建立备份
B.专机专用
C.不上网
D.定期检查
参考答案：C
______ he is only 8 years old, he knows more about science than his father. [ ]
A. But
B. Though
C. So
D. Because
垃圾有什么危害？
