定义运算$a*b=\left\{\begin{array}{c}a\left(a\le b\right)\\ b\le a>b\end{array}\right.$则函数f（x）=1*2^x的最大值为____ 

甲：“亲吾父以及人之父，以及天下人之父”，要“视天下犹一家，中国犹一人焉”

乙：“工、商皆民生之本”“天下为主，君为客”

丙：“邪辟之说灭息，然后统纪可一而法度可明，民知所从矣”

丁：“保天下者，匹夫之贱与有责焉耳矣”

    One day, a little schoolboy went home with a pain in his stomach.

    "Well, sit down and 1 a cake," said his mother."Your stomach 2hurting because it's empty.It'll be all right when you've got something in it."

    Five minutes later, Dad came home 3 the office.And he said he had a headache.

    "That's because your head is 4," said his clever son."You'll be all right if you have got 5 in it." His dad and mum laughed.