根据句意用适当的介词填空。

1. I usually download some music ________ the Internet.

2. Mr Li likes to write novels ________ the computer.

3. Bruce doesn't have a computer ________ home.

4. I always do the housework ________ the weekend.

5. Tony sometimes writes ________ his friend.

核算系统选项中的“期末结账检查未记账的单据”，是检查哪些单据？（）

A.外购入库单

B.产品入库单

C.销售出库单

D.采购订单