土壤是陆地生态系统的基础
参考答案：
生态系统包含着一个广泛的概念。任何生物群体与其所处的环境组成的统一体，都形成不同类型的生态系统。
土石方施工阶段作业昼间的噪声限值是( )dB(A)。
A．85
B．65
C．75
D．55
In order to earn money for his family, it is necessary for him to get a job.()
A. it is necessary to get a job
B. it is necessary to find a job
C. he must get a job
D. a job must be found
