Explanation:

Correct Answer is (b).The original sentence is erroneous.
Reason: Usage of the phrasal verb 'carry on' which means ‘continue an activity or task' is inappropriate in this sentence.
'Carry off' which means ‘to cause the death of’ would be suitable in this context.
E.g.: The plague carried off thousands.
Hence ‘carries off’ should be used in place of ‘carries on’ for making the sentence grammatically and contextually correct.
Among the given choices, only option B replaces the given bold part most appropriately.
The sentence after replacement becomes:
Malnutrition carries off thousands of children across the globe every year.Option B is hence the correct answer.