_____ you know English is important, you should learn it well.
A:Since
B:For
C:Because of
D:Though
世界上三大人种是____、____、____。
尿素、多余的水和无机盐,除了通过____形成尿液排出外,也能通过皮肤中的汗腺分泌汗液排出,人在运动时汗液显著增多的意义是____.