If the 20 mm rivets are used in lacing bars, then the minimum width of lacing bar should be A. 40 mm B. 60 mm C. 80 mm D. 100 mm

The correct answer is B. 60 mm.

The minimum width of a lacing bar is determined by the diameter of the rivets used. For 20 mm rivets, the minimum width of the lacing bar is 60 mm. This is to ensure that the rivets are properly seated in the lacing bar and that the lacing bar is strong enough to support the load.

Option A is incorrect because it is less than the minimum width required for 20 mm rivets. Option C is incorrect because it is more than the minimum width required for 20 mm rivets. Option D is incorrect because it is not a valid option.