in recent years __global warming is becoming __concern for people all over the world

问题描述:

in recent years __global warming is becoming __concern for people all over the world

第一个空不填,global warming 就是个环境问题,算是专有名词吧,不需要冠词.
第二个空填a,concern作名词时可以表示“关心的事”,可数,所以要加 a