Final answer:
Alpine and Saanen goats are the breeds among the given options that are seasonal breeders and tend to have single kid crops, while Boer goats have higher twinning rates and Nigerian Dwarf goats can breed year-round.
Step-by-step explanation:
The question pertains to the breeding characteristics of different goat breeds. Among the options given, the Alpine and Saanen goats are known to be seasonal breeders that typically have single kid crops. Seasonal breeders are those that mate during a certain season of the year, which in the case of goats is usually in the fall, leading to spring births. The Boer breed, while also often a seasonal breeder, is known for having higher twinning rates, thus less commonly having single kid crops. The Nigerian Dwarf goats are an exception and can breed year-round, and also commonly have multiple kids at a time. Therefore, for goat breeds that are seasonal breeders and tend to have single kid crops, Alpine and Saanen goats fit this description.