Ken lives in city C. My mom and I live in city B.
My mom: Was Ken in city B when we left for city A on 2/15?
my first response: He had already arrived at the time.
my second response: He had already arrived by then.
my third respone: He had already arrived on 2/16.
Which response is grammatically ok?
Can I use a definite time adverb (like yesterday, last month, on 2/16, etc) with past perfect tense when I want to be more specific about what time a past event happened. (of course, on the condition that a past event has been established)