联合固氮作用 associative nitrogen fixation
参考答案：
自生固氮微生物在高等植物影响下促进的固氮作用。
The small mountain village we spent our holiday last month lies in is now part of Hubei .
A．which where
B．where, what
C．that , which
D．when , which
期货交易的形式有( )。
A．实物期货
B．货币期货
C．利率期货
D．汇率期货
E．股票指数期货
