新做泥套不得超过铁口保护板，应在其内10mm～15mm为宜。
参考答案：错
生态系统中生物之间通过取食的关系而互相联系形成食物链，许多食物链互相交错形成____________。
By the time the firemen arrived, the big fire ___ for nearly half an hour. [ ]
A. had gone out
B. had been put out
C. had put out
D. had been out
