What is the permissible speed limit for a passenger car with a trailer on a road signposted as such?

In the photo there is the entrance to a town: on the right there are signs E-17a "Kłęczany" (town name) and D-42 "built-up area", and in the distance you can see sign B-33 "70". The speed limit for a passenger car with a trailer on a road marked like this is 50 km/h - answer B.

The Road Traffic Act states that the speed limit for a vehicle or vehicle combination in a built-up area is 50 km/h, and the Regulation on road signs and signals states that sign D-42 marks the entry to a built-up area. The rule speaks directly about "a vehicle or vehicle combination", so in a town a car with a trailer has the same limit as a car without a trailer; lower limits for vehicle combinations apply only outside a built-up area, where a passenger car may drive at 90 km/h, and a passenger car with a trailer only at 70 km/h. Answer A speaks of 70 km/h beyond sign B-33 - but the Regulation states that B-33 with a speed higher than 50 km/h in a built-up area applies only to a passenger car, a motorcycle and a lorry up to 3.5 t, and not to a vehicle combination; so a passenger car with a trailer has 50 km/h also beyond this sign. Answer C, 40 km/h, has no basis.

Legal basis: Art. 20 para. 1 and para. 3 point 2 and Art. 2 point 49 of the Road Traffic Act (Prawo o ruchu drogowym); § 58 para. 3 and § 27 para. 3 of the Regulation on road signs and signals