1. Read the sentences.
The Columbia River flows into the Pacific Ocean.
The Columbia River forms most of the border between Oregon and Washington.
Which choice best combines the two sentences using an adjective clause?
The Columbia River flows into the Pacific Ocean, but it forms most of the border between Oregon and Washington.
The Columbia River, which forms most of the border between Oregon and Washington, flows into the Pacific Ocean.
The Columbia River flows into the Pacific Ocean, after it forms most of the border between Oregon and Washington.
The Columbia River flows into the Pacific Ocean and forms most of the border between Oregon and Washington.