Incorrect He is sick.
Correct He is ill.
 
Incorrect I have strong headache.
Correct I have a severe headache.
 
Incorrect This is more preferable than that.
Correct This is preferable to that.
 
Incorrect No less than fifty students were present.
Correct No fewer than fifty students were present.
 
Incorrect I want a little quantity of milk.
Correct I want a small quantity of milk.
 
Incorrect Ram only is guilty.
Correct Ram alone is guilty.
 
Incorrect Do not go out in the sun with your head open.
Correct Do not go out in the sun with your head bare OR uncovered.
 
Incorrect Give a verbal translation of the passage.
Correct Give a literal translation of the passage.
 
Incorrect The association has three thousands of rupees in cash.
Correct The association has only three thousand rupees.