Verbal Ability - Selecting Words - Discussion

Herd: Number of domestic animals assembled together.

Swarm: Number of insects especially when in motion.

Group: Number of people/crowd.

Flock: Number of birds especially gathered together for the purpose of migration.

As in question cows are mentioned herd is an appropriate option!

A herd of cows, a cattle of sheep, an army of soldiers, This is called appropriate preposition in grammar.

Herd-a large group of animals, especially hoofed mammals, that live together or are kept together as livestock.

Generally, the herd is used for mammals of like a herd of cows who live together, migrate together, for livestock.

Flock is used for birds as a flock of birds sometimes it also used for goats and sheep. Swarm is used for insects.

Herd means a number of animal traveling together. So, the right answer is herd.

Thank you @Sundar.

A group of cattle or sheep or other domestic mammals all of the same kind that are herded by humans.

A herd is a large group of animals of one kind that live together.

Detailed explanation:

Herd - A large group of animals, esp. hoofed mammals, that live, feed, or migrate together or are kept together as livestock.

Group - A number of people or things that are located close together or are considered or classed together.

Swarm - A large or dense group of insects, esp. flying ones.

Flock - A number of birds of one kind feeding, resting, or traveling together.

A herd of cows is the right one.

Thanks all.