The precise origin of the measure is not definitely known.

Their precise origin and structure, however, is still under debate.

The precise origins of the decision to establish the review are unclear.

The precise origin of the name is not known.

In fact, the precise origins of the names are difficult to prove.

The precise origin of the name of the town is not known for certain.

The precise origins of the war are unknown to readers.

The precise origin of the modern burrito is not known.

In many cases, the precise origin of the poison has never been determined.

The precise origins of such a connection are unknown, however.