Hello,
In the English language, the indirect object is the recipient of the direct object.
The direct object of the sentence is the thing being acted upon.
For example, in the sentence "Sarah sliced the cake", the direct object is the cake, since that is the object which is being directly acted upon. There is no indirect object in this example since there is no recipient of the direct object (the cake).
In the sentence "Sarah sliced the cake and handed it to her sister" the indirect object would be her sister, since she is the recipient of the direct object.
The indirect object is always the recipient.
So in this case
"After a short time, he had given them enough wooden animals for three toy zoos"
The wooden animals are the direct object, since they are what is being acted upon, and the indirect object is therefore "them" since they are receiving it.
Therefore the answer is D. Them
I hope this helps.