对自然界物质循环起作用的细菌是[ ]
A．真菌
B．寄生细菌
C．腐生细菌
D．病毒
答案：C
____ has been heated discussion over which country bakes the world’ s best pizza: Italy, where pizza began or the US, where it was globalized.
A．It
B．There
C．That
D．This
饱和度
