In case of design of a shell and tube heat exchanger___________________?

A. Minimum cleaning lane of 6.5 mm is provided, when tubes are on a square pitch
B. Minimum tube sheet thickness (in which tubes are fixed) is equal to the O.D. of the tube upto
15 mm tube diameter; and for > 15 mm tube diameter, tube sheet thickness is smaller than
tube diameter
C. O.D. of the tube is 6 to 40 mm while the tube lengths used are 0.5, 2.5, 3.0, 4.0, 5.0, 6 metres
D. All A., B. & C.