A body is subjected to a tensile stress of 1200 MPa on one plane and another tensile stress of 600 MPa on a plane at right angles to the former. It is also subjected to a shear stress of 400 MPa on the same planes. The minimum normal stress will be


A. 400 MPa
B. 500 MPa
C. 900 MPa
D. 1400 MPa