You drive through Wijk bij Duurstede: first you pass a '30 km-zone' sign near a primary school, then — still within the built-up area — a street with no speed sign at all. What applies on that second stretch?
50 km/u — the ordinary built-up-area default applies as soon as there is no separate sign (anymore)
30 km/u — a 30-zone stays in force for the rest of the built-up area
30 km/u — once a sign-based exception applies anywhere in the built-up area, it stays in force for the rest of it
Explanation
False — trap: zone confusion. A 30 km-zone ends at that zone's end sign; outside that zone (but still within the built-up area) the ordinary 50 applies again (Book p.117).