A rural level railway crossing has no gates and no flashing lights — just a stop sign posted right at the tracks. No train is anywhere in sight or sound. Do you still have to make a full stop?

Correct answer: B. Yes — a stop sign at a railway crossing must be obeyed every time, not only when a train is signalled

Yes, every time, and it's a different rule from the one this might bring to mind. Section 163(1) only requires a stop when a signal device or flagman is actively warning of an approaching train. Section 163(2) covers a stop sign posted at a crossing instead, and that duty is not conditional on a train being present: "Every driver of a vehicle approaching a stop sign at a railway crossing shall... stop the vehicle at the marked stop line or, if none, then not less than five metres from the nearest rail of the railway, and shall not proceed until he or she can do so safely." A stop sign at the tracks means stop, in full, regardless of whether anything is coming.

Source: MTO Driver's Handbook: Highway Traffic Act, R.S.O. 1990, c. H.8, s. 163(2) — Stop signs at railway crossings