Read the sentence from the passage.

In the 30 years he spent exploring Africa, Livingstone covered over a third of the continent and was known for his attempt to find the source of the Nile River.

Which revision gives the sentence proper parallel structure?

A. In the 30 years he spent exploring Africa, Livingstone covered over a third of the continent and had attempted to find the source of the Nile River.

B. In the 30 years he spent exploring Africa, Livingstone covered over a third of the continent and attempted to find the source of the Nile River.

C. In the 30 years he spent exploring Africa, Livingstone covered over a third of the continent and attempting to find the source of the Nile River.

D. In the 30 years he spent exploring Africa, Livingstone covered over a third of the continent and his known attempt to find the source of the Nile River.