下列何项是青春期开始的重要标志()

A.出现厨期性排卵

B.第一次来月经

C.卵泡开始发育

D.第二性征开始出现

E.体格发育第二高峰出现

The single invention of the computer _______many new professions.

A．gave a birth to

B．gave birth to

C．gave births to

D．gave birth for