Final answer:
Mark was reserved at first but became much more communicative when he got to know us better.
Step-by-step explanation:
Mark’s reserved demeanor might have given the impression of someone withdrawn or quiet when we first met him. Perhaps he took some time to observe and understand the people around him. As he gradually felt more comfortable and developed a level of trust, he began to open up. Sometimes, individuals who seem reserved are simply cautious about revealing themselves until they feel secure or until they understand the environment they're in. In Mark's case, this initial reserve might have been a way for him to assess the situation before engaging more actively.
It’s not uncommon for people to exhibit reserved behavior in new or unfamiliar settings. Once they acclimate or build rapport, they often become more expressive and communicative. Mark's transformation from reserved to communicative underscores the importance of patience and understanding when getting to know someone new.
The correct answer is still: a) reserved.