When two components are initially tightened by a bolt with a pre load of 6 kN, the elongation of the bolt is 2 mm and the compression of the components together is 1 mm. When the assembly is subjected to 9 kN (tensile on the bolt) of external load, what will be the net compression in the components under this load? (a) zero (c) 2 mm (b) 0.5 mm (d) 1.5 mm