[mck4711]

all vul, p dealer and opens, no agreements

KQJx
KJ
J10xxx
10x

1C - p - 1D - 1NT*
p - p - 2NT** - x
3D - p - p - p

* not alerted
** here my Qs:
I considered 1NT as unusual NT, showing H and S at least 5-5, what is here the best bid: 2D (weak hand, nothing else to say), X (penalty, but might give opps opportunity to escape in H or S), 2NT (invitational, (semi-)balanced, have some values in H and S), or maybe even 2S (natural)?
I hope that my understandings of a.m. bids are ok. If not pls tell me.

edited: after 2nt there was before "minimum" - writing error, correct: invitational

P had Axxx, Q8x, K8, K98x, pity that p ran out.

BTW: LHO had 16 HCP (3 Aces, 2 Queens), and no 5-5 in S/H

[P_Marlowe]

Most important - Dont guess, what they may mean with their bids,
ask.

#1 You assumed, that 1NT was UNT, it was natural, both meanings are
common, ask, dont assume, even if you know, what he means, because
they told you we play system ABC, ask, they may have a different
meaning, what is part of ABC and what not.

#2 2NT makes no sense, if you make 2NT, do you think they make 1NT?
Your bid is either X or Pass, Pass is reasonable, if you think they
had a misunderstanding, they are red, you may or may not have game,
red undertricks in red are each worth 100, so if you get them -2,
than you will be ok (as long as your side does not make game).

#3 Because a natural 2NT is not very sensible, the bidding on by
your partner is reasonable, but he should better bid 3C, it could
be, that you have club support - 2NT in this seq. is quite often
played as Lebensohl.

With kind regards
Marlowe