当煤层节理与工作面平行时，工作面容易发生片帮事故。
参考答案：对
This is the factory _____ we worked a year ago. [ ]
A. where
B. that
C. which
D. on which
Good harvest this year has made it possible for us to supply walnuts ______ last year's prices.
A．at
B．in
C．against
D．on
