Sentence Correction

Coffee prices rose sharply Monday, posting their biggest one-day gain in almost three years, after a weekend cold snap in Brazil raised concern that there could be damage to the world's largest crop when at a time with supplies already tight.

A. that there could be damage to the world's largest crop when at a time with supplies
B. that the world's largest crop could be damaged at a time such as when supplies are
C. that the world's largest crop could be damaged at a time when supplies are
D. of the world's largest crop possibly being damaged at a time with supplies
E. of possibly damaging the world's largest crop at a time that supplies were

OA: C

Can we discuss the tenses "are" in Option C vs "were" in Option E.