stole flowers

[azz]

a. When he was a kid, he used to steal flowers from our neighbor's garden to smell.
b. When he was a kid, he used to steal flowers from our neighbor's garden to smell them

c. When he was a kid, he used to steal flowers to smell.
d. When he was a kid, he used to steal flowers to smell them.

Which of the above sentences are grammatically correct?

Wishing everybody on the forum a Happy 2019

Many thanks.