The focus of an ellipse is at the origin. The directrix is the line x=4 and its eccentricity is 12 then the length of its semi-major axis is
23
43
53
83
Directrix is x=4
Eccentricity =12
Directrix =[ae–ae]=4
⇒ae–ae=4⇒a[1e–e]=4⇒a[12-2]=4⇒a×32=4∴a=83
Hence, the length of its semi-major axis is 83
Hence, the correct option is D.