Difficulties
n. 困難( difficulty的名詞復數 ); 難度; 難事; 麻煩
??? 情景例句
It's for a book.
是為一本書拍的。
He likes playing at the model buiding.
他喜歡玩摸型建筑。
The further off this solid obstruction, the longer time will elapse for the return of the echo.
固體障礙物越遠。回聲返回所用時間就越長。