Comment on the comment by V.A.F. Costa, IJTS 49 (9) (2010) 1874-1875, on the paper by I. A. Badruddin, Z. A. Zainal, Z. A. Khan, Z. Mallick "Effect of viscous dissipation and radiation on natural convection in a porous medium embedded within vertical annulus", IJTS 46 (3) (2007) 221-227