In the above sentence, 'trying' has not been used as a noun in the sentence because it is related to some work which is happening. Hence, it cannot be considered a gerund. In the sentence, the noun is the men who are still trying to complete the work which has started yesterday. This shows an ongoing activity at the time when this sentence is spoken by a person. Hence, 'trying' becomes a present participle and not a past participle. Option A) is therefore the right option.