Final answer:
The most likely conclusion from Mackay's diary entries is that he knew several of the people who were injured or died in battle. We can ascertain that Mackay was familiar with those who had been injured or died, as indicated by his intention to write to MacCallum's girl and his listing of several names alongside their conditions.
Step-by-step explanation:
Based on the sentences from Mackay’s diary entries, it is clear that Mackay was affected by the news of injuries and deaths among his colleagues. We can ascertain that Mackay was familiar with those who had been injured or died, as indicated by his intention to write to MacCallum's girl and his listing of several names alongside their conditions. Therefore, the most logical conclusion drawn from this evidence is that Mackay probably knew several of the people who were injured or died in battle.