Which sentence is the correct one?

Correct Sentences: 
Had I affluence! (had এর Object হিসেবে Noun থাকা বাঞ্ছনীয়।) 
I don’t understand where the problem lies. (Sub-ordinate Clause (where the problem lies) সর্বদা Assertive Form এ বসে।
That they are worthless are understood by all. (Clause (That they are worthless )– Subject হলে তা সব সময় Singular হয়।) 
Let your opponents criticise you and you will understand your mistakes. এটাই নির্ভুল বাক্য।