Everybody should _____ their old parents.

White elephant - ব্যয় সাপেক্ষ, অর্থাৎ A very costly and troublesome possession ।

"apple of one's eye" means an extremely favourite or cherished person who is loved and prized above all others.

A cock and bull story means a false, absurd, or ridiculous story that is completely untrue, often invented and told as an unconvincing excuse or explanation. 

The interrogative form of "All love flower" is Who does not love flower?.

The assertive form of the sentence is: It is a very nice scenery.

- Only যুক্ত Affirmative sentence-কে Negative করার সময় Only-এর পরিবর্তে none but (ব্যক্তির ক্ষেত্রে) বসে।
- প্রদত্ত বাক্যে 'Only' শব্দটি 'Rina' (একজন ব্যক্তি)-কে নির্দেশ করেছে।
- তাই Only-এর জায়গায় None but বসবে।
- সুতরাং সঠিক Negative বাক্য: None but Rina can do this sum.