Answer: B
Correct answer: was present
A phrase introduced by along with, as well as, together with, besides, in addition to or accompanied by does not change the number of the subject. The subject here is the manager, singular, so the verb is was. These phrases are parenthetical - usually set off by commas, as here - and can be removed without damaging the sentence: the manager was present. That removal is the quickest test. Contrast this with and, which genuinely creates a compound plural subject: the manager and his assistants were present is correct. The distinction is a favourite of examiners precisely because the plural noun sits next to the verb and the ear supplies the wrong agreement.