--Thiskindofsportsisexciting．   --Yes，butit'sdangerous．...

問題詳情：

--This kind of sports is exciting．

    --Yes，but it's dangerous．One can't do it ____ he or she has got some training．

A．if              B．after             C．when            D．Unless

【回答】

D

知識點：連詞

題型：選擇題