考查近义动词的语义及搭配用法。各选项的意思及用法是：选项A)separate使分开，区分，区别，常用结构是"separate A from B"。如：separate cause from effect区分因果关系;选项B)isolate使隔离，使孤立，常用于isolate…from结构中。如：Several towns have been isolated from the outside world by the flood.有好几个城镇因洪水与外界隔绝了。选项C)contrast对比，对照，常用于"contrast A with B"结构中。如：contrast Europe with America将欧美两洲做一番比较;选项D)distinguish区分，辨别，常用于"distinguish A from B/distinguish between A and B"结构中。如：distinguish between right and wrong/distinguish right from wrong明辨是非。根据题干中的介词及句意，可判断出选项D)应为正确答案。全句意思为“众所周知，色盲的人很难区分红色与绿色”。