Final answer:
The correct sentence is 'A lot of errors were found in the final report,' which uses past passive voice to show that the errors were found by someone else. 'Were found' is the past passive form needed to complete the sentence grammar correctly.
Step-by-step explanation:
The correct answer to the question "A lot of errors _____ in the final report" is a. were found. This sentence requires a past passive verb because the errors are the object of the action and they are not performing the action. The errors were found by someone.
In the sentence provided, 'errors' is the subject, and since the sentence is written in passive voice, we use the verb 'were' followed by the past participle of 'find,' which is 'found.' The correct past passive construction of the sentence is, therefore, 'A lot of errors were found in the final report.' This grammatically correct choice indicates that the action was done by someone else (in this case the action of finding), rather than the errors finding something themselves, which would not make sense.
The other options, 'found,' 'find,' and 'be found,' are incorrect because they do not provide a complete and coherent past passive verb structure needed for this sentence.