The student worked ________, but, to our disappointment, he still failed in the final examination．
A.as hard as possibleB.as hard as possiblyC.as hard as he canD.so hard as he could在线课程A
表达“尽可能……”时，可用“as…as possible”或“as…as sb．can/could”。从本句中动词所表示的时间来看，结构中应用过去时态，故排除C项。