We have't heard from David since he left Shanghai.(对划线部分提问,划since he left Shanghai）
问题描述：
We have't heard from David since he left Shanghai.(对划线部分提问,划since he left Shanghai）
答
How long haven't you heard from David?How much are these vegetables?(保持句意不变）=How much do these vegetables cost?=What's the price of these vegetables?