A cat, ______ it is a white one ______ a black one, is considered to be a good cat as long as it can catch mice.

A．both; and

B．not only; but also

C．either; or

D．whether; or

微量元素是指

A．人体含量很少的元素

B．食物中含量很少的元素

C．自然界含量很少的元素

D．人体吸收率很低的元素

E．人体利用率很低的元素