A deer is a mammal, so reproduction is done internally.
internally
externally
internal
That depends on the species you are asking about, mammals fertilize internally and fish externally.
Guppies are fertilised internally they are livebearers.
internally because they need time to hatch them
Amphibians fertilize their eggs externally.
Koalas do not fertilize their young. They fertilize each other (internally) to produce young.
Internal fertilization
true
No. Fishes fertilize externally.
Most fish eggs develop outside of the body. There are however around 3% of all fish which fertilize internally.