Which sentence is a simple sentence?

a.
i enjoy fishing, but i get seasick in boats.

b.
before the trip, i had never been to a national park.

c.
my dog has spots; hers does not.

d.
before the train came to a halt, its brakes squealed loudly.

particulars about treasure island, from the beginning to the end, keeping nothing back but the bearings of the island, and that only because there is still treasure not yet lifted, i take up my pen in the year of grace and go back to the time when my father kept th

explanation:

it took the same time to travel by as it did on   train : ) hope i