The H7N9 bird flu is a disease ______ can be very dangerous.A./ B.who C.what D.which （请说明理由）
问题描述：
The H7N9 bird flu is a disease ______ can be very dangerous.A./ B.who C.what D.which （请说明理由）
答
选D which作为连接词把两句话接起来的.这里which指代bird flu.