"...picked from his garden" is follwed by "in a vase" which implies that "garden in a vase". Hence incorrect construction

A, D & E are out

B implies is wordy and awkward.

C is the best choice

Hence answer is C

A, E - pronoun error
B - parallelism had been ... and was
D - awk

Khurram,
As i understand, we all use the website not just to learn but practice also.
So 2 requests to you /
1. Always underline the part of the sentence to be corrected.
2. Dont mention the OA in the first post itself or if you do, pls mark it as black ..so that it is not visible...

Usually human eyes are not master in reading only the first few lines and skipping the others ..whatever comes in span is read .. and knowing the answer doesnt helps in making a honest attempt ..!

D is wrong because
To make our sentence correct with "during," we'd need to add some information that would identify which two decade-period we are talking about.Eg:Even though its per capita food supply hardly increased during the two decades between 1940
and 1960...
I hope it clears your doubts regarding D