Elsie is seventy years old and a fanatical gardener.

Answer: Option C

Crazy : mad, especially as manifested in wild or aggressive behaviour.
Fantastic : extraordinarily good or attractive.
Enthusiastic : having or showing intense and eager enjoyment, interest, or approval.
Obsessed : preoccupy or fill the mind of (someone) continually and to a troubling extent.
Fanatical : obsessively concerned with something.

Synonym of Fanatical is Enthusiastic