First Principles Thinking: governing standard
A is correct. Standard III(B) requires that new issues be distributed to clients for whom the investment is appropriate, and, when oversubscribed, prorated to suitable accounts on a round-lot basis. Suitability is therefore a gating filter; fairness is measured among eligible accounts, not by forced inclusion of unsuitable accounts.
B is tempting because candidates memorize 'pro rata to all who indicated interest,' but the Curriculum conditions pro-rata allocation on the trade being appropriate for the account.
C fails because the Standard does not impose a consent-to-exclude requirement. Exclusion on suitability grounds is driven by the client's mandate, not by case-by-case consent.