While some economists believe that Germany

While some economists believe that Germany should be warned by the European Commission that it could face the imposition of radical restrictions on its domestic fiscal policymaking as early as the beginning of next year, others say that Germany will take the warning seriously only if it would be backed by sanctions.  

A.  only if it would be backed by sanctions.  
B.  only if it is backed by sanctions.  
C.  if it is backed only by sanctions.  
D.  if it was only backed by sanctions.  
E.  if it would only be backed by sanctions.  

The best answer is B. In sentences expressing a conditional result (X will happen if Y happens), the verb of the main clause should be in the future tense and the verb of the if clause should be in the present indicative. Thus, is backed (in B) is consistent with will take.