The answer is d unless you messed up typing
It doesnt make much sense so it has to be false
It should be "I will be" because this sentence is past tense. Meaning the "I will be" would be in the future. And since those are the answers 'I will be' would be the the answer. Which means the sentenced corrected would be: I was happy to help you in the garden when I came to visit you last month.