The tread depth of a steering tire should be no less than _____ millimetres.

Answer: B — 3.2

The ideal tread depth of a steering tire should be no less than 3.2 millimeters. This allows for proper traction and grip on the road while turning and maneuvering the vehicle. Options A, C, and D all have tread depths that are either too shallow (A and C) or dangerously low (D). A tread depth of 4.0 millimeters (A) is still acceptable but may not provide optimal traction, especially in wet or slippery conditions. A tread depth of 5.5 millimeters (C) may provide better traction, but it is not necessary and may be considered excessive. A tread depth of 2.5 millimeters (D) is below the legal limit in many countries and can compromise safety on the road.