Which revision best uses subordinating conjunctions to clarify the meaning of this passage?

Siobhan couldn't figure out how to end the short story she was writing. She would get a poor grade. Siobhan spent the day lost in thought at the lake. She finally knew how to end it.

A. Because Siobhan couldn't figure out how to end the short story she was writing, she would get a poor grade. Siobhan spent the day lost in thought at the lake, so she finally knew how to end it.

B. If Siobhan couldn't figure out how to end the short story she was writing, she would get a poor grade. After spending the day lost in thought at the lake, she finally knew how to end it.

C. Despite Siobhan's being stuck on the short story she was writing, she would get a poor grade. Before she spent the day lost in thought at the lake, she finally knew how to end it.

D. Although Siobhan couldn't figure out how to end the short story she was writing, she would get a poor grade Siobhan spent the day lost in thought at the lake, because she finally knew how to end it​