The correct answer is: C. 4.5 m
A couple close roof is a type of roof that is made up of two pairs of rafters that are connected at the top by a ridge board. The rafters are then supported by purlins, which are horizontal beams that are attached to the walls of the building. The couple close roof is a very strong and stable roof, and it is suitable for spans of up to 4.5 m.
Option A (2.5 m) is not a suitable span for a couple close roof. This is because the rafters would be too close together, and the roof would not be strong enough to support the weight of the roof covering.
Option B (3.5 m) is a possible span for a couple close roof. However, it is important to note that the rafters would need to be reinforced in order to support the weight of the roof covering.
Option C (4.5 m) is the most suitable span for a couple close roof. This is because the rafters would be far enough apart to be strong enough to support the weight of the roof covering, and they would not need to be reinforced.
Option D (5.5 m) is not a suitable span for a couple close roof. This is because the rafters would be too far apart, and the roof would not be strong enough to support the weight of the roof covering.