the other side of the board should be painted white = the other whiteA: 谓语动词'should be painted'不能被换成'is',可以换成'should be'B、D:side 暗示只有两边,用'another'不恰当
完整的应该是the other should be painted white, 和前面的谓语相同,避免重复而省略。
A