The Dittus$-$Boelter equation for convective heat transfer $[($i$.$e$.$ h $=0\mathrm{.}023($K$/$D$)($Re$)0\mathrm{.}8($Pr$)0\mathrm{.}8]$ cannot be used for

Low Reynold's number

Very low Grashoff number

Molten metals

All $($A$),($B$)$ and $($C$)$