— Must I five the dictionary back to the library now? 

— No, You _____. You can _____ it for another two weeks. [ ]

A. needn't, know

B. needn't, keep

C. mustn't, lend

D. mustn't, keep

某个电脑用户计划使用不超过1 000元的资金购买单价分别为80元、90元的单片软件和盒装磁盘.根据需要，软件至少买3片，磁盘至少买4盒，写出满足上述所有不等关系的不等式.