并列句子。。。需不需要逗号的问题

sunshinemuji

Last week it warned it would not be able to guarantee the safety of foreign embassy staff after 10 April, and that countries should begin evacuating their diplomatic staff

我老有个疑惑，就是并列的成份之间什么时候可以用and连接？什么时候可以用 “，and"连接？  就像上句为什么不直接用and连接呢

sunshinemuji

那用and连接两个句子，可以有省略吗？
North Korea has told foreign embassies in Pyongyang it cannot guarantee their safety in the event of conflict, and to consider evacuating their employees

sunshinemuji

那用and连接两个句子，可以有省略吗？也就是说下句可以去掉逗号不？
North Korea has told foreign embassies in Pyongyang it cannot guarantee their safety in the event of conflict, and to consider evacuating their employees