1．If the new safety system (bring) into use, the accident would never have happened.
had been brought 解析：句意：如果新的安全系统已经投入使用，事故就不会发生了。根据句意、句子结构以及主句中的would never have happened可知，句中If引导的是虚拟条件句，且表示与过去的事实相反的假设，故从句时态应用过去完成时。
2．When you phoned me, I was having a meeting; how I wish I (answer) your call.
had answered 解析：句意：当你给我打电话的时候，我正在开会。我多么希望我(之前)接了你的电话。wish后的从句中用虚拟语气，根据句意可知是对过去情况的虚拟，所以谓语动词用had done形式。
3．As the deadline is drawing near, no one leave with his own work uncompleted.
shall 解析：句意：因为截止日期即将到来，不完成工作，任何人不许离开。shall用于第三人称陈述句中，表示命令、警告，符合句意。
4．The order came that the medical supplies (send) to the earthquakestricken area soon.
(should) be sent 解析：表示建议、要求、命令等名词，如：suggestion, order, request, advice等后接的表语从句、同位语从句中谓语动词用(should＋)动词原形。
5．It is high time that you (consider) that if there were no stress in your life, you would achieve a little.
considered/should consider 解析：在It is high time that...句式中，从句用虚拟语气，即：谓语动词用过去式或should＋动词原形。
