GMAT Sentence Correction (SC) | Several studies have found that the coronary patients who

Isn't it "likely to" a correct idiom? Can "likely" stand alone without "to"? I thought "likely" had to be follwed with "to" all the time, like in the example link below ? What makes the answer E more right than D? Can someone please explain?
according-to-a-survey-of-graduating-medical-students-80213.html