Identify the sentence that correctly uses the indefinite article.

Cloud seeding involves use of chemicals that target rain-bearing clouds above a catchment area such as an river, reservoir or an lake.

Cloud seeding involves use of chemicals that target rain-bearing clouds above a catchment area such as a river, reservoir or a lake.

Cloud seeding involves use of chemicals that target rain-bearing clouds above an catchment area such as a river, reservoir or an lake.

Cloud seeding involves use of chemicals that target rain-bearing clouds above an catchment area such as an river, reservoir or a lake.