The correct answer is option A.
We have to identify the correct option that correctly describes the manner in which they recognized each other.
Option B-HARD is an adjective and therefore does not describe the manner if recognition.
Option C-MUCH is a determiner and is usually used to indicate quantity and used with the word BETTER.
Option C- RATHER is used to indicate preference.
None of the options describe the manner in which they recognized each other. Thus they are incorrect options.
Option A HARDLY correctly describes the manner in which they recognized each other. Since they met after a long time they could not really recognize each other well.
Option A is the correct answer.