If you are on the beach and are signaling to a small boat in distress that your present location is dangerous and they should land to the left，you would（）.

A.fire a green star to the left

B.send the letter K by light and point to the left

C.place an orange signal to your left as you signal with a white light

D.send the code signal S followed by L

工业化施工的内容就是把预制加工并经过试验的管道______安装成______。