had better表示""，相當(dāng)于一個助動詞，它只有一種形式，它后面要跟動詞原形。例如：
    It is pretty cold. You'd better put on my coat. 天相當(dāng)冷。你穿上我的外套。
    She'd better not play with the dog. 她不要玩耍那條狗。
    had better have done sth表示與事實相反的結(jié)果，意為"本來".例如：
    You had better have come earlier. 你本該來得早一點。