Realist authors write their stories a bit more real (hence REAList) So if you review your answers...
D. Depict the beauty of nature.
They could do this but not all realist authors write about nature.
C. Use figurative language.
Figurative language is usually used to make stories exciting and add words and comparisons and phrases that aren't real. They just replace original real sentences so this isn't the correct answer.
B. Use imagination more.
This clearly isn't it because imagination isn't real.
A. Depict life as it really was. This is correct because realist authors write stuff as they really were.
Hope this helped!