下列说法正确的有(填序号):____ .
①同位角相等;
②一条直线有无数条平行线;
③在同一平面内,两条不相交的线段是平行线;
④在同一平面内,如果a∥b,b∥c,则a∥c;
⑤过一点有且只有一条直线与已知直线平行.
— It's dangerous to swim in this river.
—Yes, you are right. The government has ______ people not to swim in it.
读图回答问题
下列对感应电流大小无影响的因素是( )