The desert today / be characterized / 700 - foot - high dunes / giant sand mountains.

• A. 
  The desert today is characterized with 700 - foot - high dunes but giant sand mountains.
• B. 
  The desert today is characterized by 700 - foot - high dunes and giant sand mountains.
• C. 
  The desert today is characterized by 700 - foot - high dunes and however giant sand mountains.
• D. 
  The desert today which is characterized by 700 - foot - high dunes and giant sand mountains.