某鸡场有公鸡x只，母鸡数是公鸡数的7.5倍，母鸡有（ ）只，如果公鸡和母鸡共340只，列方程为（ ）。
7.5x；x+7.5x=340
“How was ______ they discovered the entrance to the underground palace？” “Totally by chance.”
A．it that
B．he that
C．it when
D．he which
1978年关于真理标准问题大讨论的历史意义是什么？
