He has been back .
I will never forget that terrible accident _______ it happened so long ago.
---- I think science is more useful than art. ---- I disagree. I think art is _________ science.
---- Do you know how to prevent the A/H1N1 flu? ---- You can ask the doctor for some ________.
The students enjoy Miss Yang’s classes because she’s a teacher with rich teaching _________.
Jim received a present from his friend, but he didn’t _________ it.