单项选择题
A light used to signal passing intentions must be an （）.
A.all-round yellow light only B.all-round white light only C.all-round blue light only D.alternating red and yellow light
单项选择题 A light signal consisting of three flashes means （）.
单项选择题 A liferaft which has inflated bottom-up on the water（）.
单项选择题 A lifeline must be connected to the liferaft （）.
