完形填空i believe you bought a ticket.all right.you don't_______

完形填空
i believe you bought a ticket.all right.you don't_________buy an other ticket," said the conductor kindly.but mr.brown________ looked worried."you don't know why.if i find my ticket,i can _______where i should go.
(1)
a.must
b.can
c.have to
d.may
(2)
a.still
b.already
c.yet
d.never
(3)
a.hold
b.forget
c.see
d.remember
why?