The correct option is
D castigate
Option D: 'Castigate' means 'to criticize someone or something severely'.
Here, the sentence means that 'it is easy to criticize English medium education but impossible to replace it'.
The word forms a complete meaningful sentence and hence option D is correct.
Option A: 'Deny' means 'refuse to admit the truth or existence of'.
Option B: 'Approve' means 'agree to or accept as satisfactory'.
Option C: 'Propagate' means 'spread and promote widely'.
Option E: 'Eliminate' means 'completely remove or get rid of (something)'.
These words do not form a complete meaningful sentence.
Hence options A, B, C and E are wrong.