船舶报告系统的一般原则中规定船舶报告系统通信费用是（）.

A.按照通信时间付费

B.免费

C.按流量付费

D.按发送途径不同而不同

Timmy goes to school _____ every day. It's 5 minutes' walk from his home to school. [ ]

A. in a bus

B. by MTR

C. on foot

D. by train