撒哈拉以南非洲农业生产落后的历史根源是[ ]

A．历史短，起步晚

B．长期被欧洲殖民统治

C．人口增长过快

D．出口初级产品为主

Sub-contractors should obey the contractor in information system project. When censoring sub-contractors, the supervisor mostly concerns about ______.

A．Amount of subcontract

B．qualifications and abilities of sub-contractors

C．responsibilities and obligations of sub-contractors

D．the contents of the subcontract