照花前后镜,____。____,____。(温庭筠《菩萨蛮》)
当今世界,各国之间激烈的竞争,归根到底是( )
I have no difficulty __________ writing, but I have some difficulty __________ pronunciation.
用反证法证明“已知平面内的三条直线a,b,c,若a∥b,c与a相交,则c与b也相交”时,第一步应该假设____