秦始皇修筑长城是为了用来抵御_________。为了开发东南和岭南地区，兴修了_________，沟通了长江水系和珠江水系。

_____ to work, Bob bumped into an old friend, David, who he hadn't seen for years.[ ]

A. On the way

B. In the way

C. In a way

D. Out of the way