A:let him to go home
B:to let him go home
C:let him go home
D:to let him to go home
填表.(从左到右填写)
(Ⅰ)求f(t)的单调减区间;
(Ⅱ)求证:f(t)+f(t+2)+f(t+4)是定值.
造成“背斜成山,向斜成谷”的主要地质作用是( )
把一根柔软的螺旋形弹簧竖直悬挂起来,使它的下端刚好跟杯里的水银面相接触,并使它组成如图所示的电路图,当开关S接通后,将看到的现象是()