请问that 代表什么,and often do 是什么成分

请问that 代表什么,and often do 是什么成分the rate do B would be twice that for A.还有一个问题,the temperature control problems can and often do occur.怎么翻译,and often do 是什么成分,do 和 occur 都是动词,能连用吗,the rate of B would be twice that for A.改成the rate of B would be twice that of A.可以吗