In a perfectly competitive market, prices and production costs are kept ?

Firms
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Varied.

Explanation:

Market is a place whereby buyers and sellers meet, in which sellers provides goods and services to the buyers in exchange for money. There are some markets in which there are few sellers of a particular goods and services(or many sellers with different goods and services and the kind of market is known as monopolistic competitive market) and there are also some markets in which we have numerous buyers and sellers.

When there are many or numerous buyers and sellers in a market we say that the market is a PERFECTLY COMPETITIVE MARKET.

The other characteristics apart from the numbers of buyers and sellers of perfectly competitive market is that "prices and production costs are kept" varied because there is no access to price control.

Hunter-gatherer societies are the earliest inhabitants of the famous fertile crescent in South East Asia whose knowledge and skills in hunting and gathering during the Neolithic age contributed immensely in support of the growing society. It's not until 10,000 years ago when these societies began to practice domestication of plants and animals due to population pressure and sometimes the migration of wild animal.