生物的多样性包括__________多样性、__________和__________多样性。
物种；遗传；生态系统
片剂的松片主要通过（）、增加黏合剂用量或浓度予以解决。
---I’m sorry to have kept you waiting long.
---Never mind. I ____ here for only a few minutes.
A．have been
B．have come
C．have arrived
D．waited
