人民民主专政的本质是(  )

A．工人阶级领导

B．工农联盟为基础

C．人民当家作主

D．坚持社会主义

As there is less and less coal and oil, scientists are exploring new ways of making use of （）energy, such as sunlight, wind and water for power and fuel.

A. primary

B. alternative

C. instant

D. unique