part b

It helps to keep the place warm

part a)

The stadium is based around a bowl design with a capacity of 90,000, protected from the elements by a sliding roof that does not completely enclose it. It can also be adapted as an athletic stadium by erecting a temporary platform over the lowest tier of seating ^{[citation needed]}. The stadium's signature feature is a circular section lattice arch of 7 m (23 ft) internal diameter with a 315 m (1,033 ft) span, erected some 22° off true, and rising to 133 m (436 ft). It supports all the weight of the north roof and 60% of the weight of the retractable roof on the southern side.^[6] The archway is the world's longest unsupported roof structure.^[7] Instead of the 39 steps climbed, in the original stadium, to enter the Royal Box and collect a trophy, there are now 107.^[8]