Which sentence contains an inappropriate shift in tense?

A.
I finished painting the fence, but Barbara is still repairing the gate.

B.
Hummingbirds are hovering over the geraniums while caterpillars munched leaves.

C.
I am reading a poem that was written thousands of years ago.

Question

Which sentence contains an inappropriate shift in tense?	
 
 A.
I finished painting the fence, but Barbara is still repairing the gate.
 
 B.
Hummingbirds are hovering over the geraniums while caterpillars munched leaves.
 
 C.
I am reading a poem that was written thousands of years ago.

solomonzelman · Answer

structures:
~   "did, but still doing"                               (good)
~   "...are doing, while ... did"                      (bad)
~   "doing something, that ... years ago"       (good)