Four abbreviations have been given, out of which three are alike in some manner and one is different. Select the odd one.

Let's analyze all the options:

(a) CRPF (Central Reserve Police Force) → A paramilitary force under the Ministry of Home Affairs.
(b) BSF (Border Security Force) → A paramilitary force responsible for border security.
(c) NDA (National Defence Academy) → A training institute for the armed forces.
(d) ITBP (Indo-Tibetan Border Police) → A paramilitary force responsible for guarding the Indo-Tibetan border.
Odd One:
CRPF, BSF, and ITBP are all paramilitary forces. 
NDA is a training academy, not a paramilitary force. 
Therefore, NDA is the odd one out.

Thus, the correct option is (c) NDA