By looking at a plant externally,can you tell whether a plant is $C_{3}$ or $C_{4}$? Why and how?

(N/A) No,one cannot distinguish whether a plant is $C_{3}$ or $C_{4}$ simply by observing its external morphological features.
$C_{4}$ plants possess a unique leaf anatomy known as $Kranz$ anatomy,which involves the presence of bundle sheath cells surrounding the vascular bundles.
This anatomical difference is internal and can only be observed at the cellular level using a microscope.
External appearance does not reveal these internal structural arrangements.
For instance,both wheat and maize are grasses,but wheat is a $C_{3}$ plant,whereas maize is a $C_{4}$ plant.