(i) and (iii)

(i)and(iv)

(ii) and (iii)

(ii) and (iv)

forces of tension and compression change but lever arm remains unchanged

forces of tension and compressions remain unchanged but lever arm changes with the moment

both forces of tension and compres-sion as well as lever arm change

both forces of tension and compres-sion as well as lever arm remain unchanged

to provide adequate bond stress

to resist tensile stresses

to impart initial compressive stress in concrete

all of the above

upper part of the beam

lower part of the beam

center

anywhere

Long line method

Freyssinet system

Magnel-Blaton system

Lee-Macall system