serial half adder

例句：

1. 1. The serial number of the watch is 123456789.
   手表的序列号是123456789。
2. 2.They are working on a serial project that will take several months to complete.
   他们正在从事一个需要几个月才能完成的连续项目。
3. 3.The serial numbers of the books were written in neat rows on the shelves.
   这些书的序号整齐地写在书架上。