We were dancing to ____ music when all of ____ sudden the power went out and we were left in the dark.

A．the; a

B．the; /

C． a; /

D．/; the

锂和钾两种元素相比较，正确的是

A．锂的还原性比钾的弱

B．锂原子的半径比钾的大

C．锂的金属性比钾的强

D．锂单质的熔点比钾的低