—_______, but I'm full now.
A:You're kidding
B:I'm sorry to hear that
C:Sorry, I can't
D:Thanks a lot
—Look! How _________ the market is!—Yes. There are always lots of people buying things there.
书放在水平桌面上,桌面会受到弹力的作用,产生这个弹力的直接原因是( )