The shop manager always says to his clerks,“We can never be___________ polite to our customers.”
A.soB.fairlyC.tooD.rather在线课程C
解析：
can never be too polite“无论怎么礼貌都不为过”或者“越有礼貌越好”。can not(never)…too…再怎样也不过分。