Some distance after a "do not pass" sign, you come to a white square sign carrying a green permissive symbol, sometimes with a small tab reading "PASS WITH CARE". What does it mean?

Correct answer: A. The no-passing zone has ended — passing is permitted when you judge it safe

The no-passing zone has ended. Book 5 states that the purpose of the PASSING PERMITTED sign "is to inform motorists that they are no longer in the no-passing zone indicated upstream by the DO NOT PASS sign and that passing is permitted when safe to do so," and it "must be used only at the end of a no passing zone that is properly signed with the DO NOT PASS sign." The PASS WITH CARE tab is added where drivers may not yet recognise the symbol on its own. Read the last clause carefully: the sign lifts a prohibition, it does not tell you the road ahead is clear. Judging the gap, the sightline and the oncoming traffic is still entirely yours, and the pavement markings will agree with the sign.

Source: MTO Driver's Handbook: Ontario Traffic Manual, Book 5 — Regulatory Signs (December 2021), PASSING PERMITTED Sign (Rb-35) and PASS WITH CARE Tab Sign (Rb-35t)