The correct answer is: Grandfather was digging the flowerbeds.
In this sentence, “grandfather” is the subject and “was digging” is the verb. The object of the sentence is “flowerbeds.” This means that grandfather is the one who is doing the digging, and the flowerbeds are the thing that is being dug.
The other options are incorrect because they do not accurately reflect the meaning of the sentence. Option A, “The grandfather was digging flower beds,” is incorrect because it does not specify that the grandfather is the one who is doing the digging. Option B, “Grandfather’s flowerbeds were being dug,” is incorrect because it does not specify who is doing the digging. Option C, “The flowerbeds were being dug by grandfather,” is incorrect because it does not specify that the grandfather is the one who is doing the digging. Option D, “The flowerbeds were digging grandfather,” is incorrect because it does not make sense.