半圆柱体P放在粗糙的水平地面上，其右端有固定放置的竖直挡板MN，在P和MN之间放有一个光滑均匀的小圆柱体Q，整个装置处于静止状态，如图所示是这个装置的截面图，若用外力使MN保持竖直且缓慢地向右移动，在Q落到地面以前，发现P始终保持静止，在此过程中，下列说法中正确的是 （   ）

世界上华人和华侨分布最集中的地区在（    ）

完成对话
A: How was your vacation, Fred?
B: ____ .
A: ____ ?
B: I went to the U.S. with my parents.
A: Cool! ____  in the U.S.?
B: First we went to Los Angeles(洛杉矶). My uncle lives there. Then we went to New York to see my cousin.
A: ____ ?
B: It was a little warm but sunny.
A: Did you see any movie stars in Los Angeles?
B: No, but I saw Tom Cruise in New York. He was at a restaurant! I got his autograph.
A: Wow! That’s great!  What else did you do in New York?
B: Hmm…Oh yeah, I also went to Central Park.____ there! .