There's no way of knowing why one man makes an important discovery ________ another man, also intelligent, fails.
A:since
B:if
C:as
D:while
如图所示,有一种新型节能路灯,它“头顶”风扇,“肩扛”太阳能电池板,并有蓄电池可以日夜蓄能.关于它的设计下列解释合理的是( )
函数y=ax﹣2+1(a>0且a≠1)的图象恒过定点____.