19. --- Could you tell me how the sea sand comes about ? --- Sea waves dash against the rock. In this way , the sea sand ___ .
Professor Hawking stepped into the office I knew that there was no hope.
Usually children are allowed to ___________ when they are six years old.
.Our team was ahead during the first half, but we _____ in the last ten minutes.
It is the first time that I ___ this kind of moon cake.
While listening carefully, the students___ what their teacher said.