[填空题]
What is the linear speed ofak4j 1 bnr-f ybzv0;qb-fc 6m0 a point6vt e7cw. e9q kzt;b/t (a) on the equator, $m/s$ (b) on the Arctic Circle (latitude 66.5$^{\circ} $ N), $m/s$ (c) at a latitude of 45.0$^{\circ} $ N, due to the Earth’s rotation? $m/s$