给出命题：

①异面直线是指空间既不平行又不相交的直线；

②两异面直线a，b，如果a平行于平面α，那么b不平行平面α；

③两异面直线a，b，如果a⊥平面α，那么b不垂直于平面α；

④两异面直线在同一平面内的射影不可能是两条平行直线．

上述命题中，真命题的序号是______．

28.The comedy Tooth Fairy is based on the story all western children know: If a kid leaves a tooth under their pillow, they’ll receive a visit from the tooth fairy, who takes the tooth and leaves a gift ________.

A．in general

B．in exchange

C．in total

D．in common