Which of the options correctly combines the following two given sentences without changing the meaning? The old books were very difficult. The new books are very simple.

• A.  If the old books are very difficult, the new books are very simple.
• B.  Whereas the old books were very difficult, the new books are very simple.  
• C.  Although the old books were very difficult, the new books are very simple.
• D.  When the old books are very difficult, the new books are very simple.