In a short cylindrical external mouthpiece, the vena-contracta occurs at a place which is at a distance equal to

A

diameter of the orifice from the outlet of orifice

B

one-fourth the diameter of the orifice from the outlet of orifice

C

one-third the diameter of the orifice from the outlet of orifice

D

two-third the diameter of the orifice from the outlet of orifice