When/ I arrive/ lecture/ already start/ professor/ write/ overhead projector//

A. When I arrived the lecture already started and the professor wrote the overhead projector.

B. When I arrived lecture had already started 'and professor wrote the overhead projector.

C. When I arrived the lecture had already started and the professor was writing on the overhead projector.

D. When I arrived the lecture had already started and the professor had writing on the overhead projector.