\begin{tabular}{|l|l|}
\hline Q.21 & $\begin{array}{l}\text { Consider incompressible laminar flow of a constant property Newtonian fluid in } \\
\text { an isothermal circular tube. The flow is steady with fully-developed temperature } \\
\text { and velocity profiles. The Nusselt number for this flow depends on }\end{array}$ \\
\hline & \\
\hline
- & neither the Reynolds number nor the Prandtl number \\
\hline - & both the Reynolds and Prandtl numbers \\
\hline - & the Reynolds number but not the Prandtl number \\
\hline - & the Prandtl number but not the Reynolds number \\
\hline & \\
\hline
\end{tabular}