It is reported that the United States uses_________ energy as the whole of Europe.

A．twice as

B．twice as much

C．twice as many

D．much twice as

维持血钙正常水平最重要的调节因素是（）

A.甲状旁腺激素

B.降钙素

C.维生素D

D.1，25-（OH）₂-D₃

E.甲状腺素