单项选择题
A line of position derived from a loran reading is a section of a(n) （）.
A.straight line B.arc C.parabola D.hyperbola
单项选择题 A light used to signal passing intentions must be an （）.
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（）.
