কোন বানানটি শুদ্ধ?

'ago' এখানে verb কে modify করছে,  তাই adverb হিসেবে গণ্য হবে।

"Beauty is truth, truth beauty" was written by English Romantic poet John Keats. The famous line appears in the closing stanza of his 1819 poem, "Ode on a Grecian Urn," concluding with the immortal lines: "That is all ye know on earth, and all ye need to know."

"At least one of the students --- full marks every time" বাক্যে শূন্যস্থানে সঠিক শব্দটি হবে gets, কারণ 'one' এখানে Subject হিসেবে singular, তাই verb-এর সাথে 's' যুক্ত হবে এবং 'every time' (প্রতিবার) থাকায় Present Simple Tense ব্যবহৃত হবে, তাই উত্তর হবে "gets" (খ). 

"Fetch some water for me" is completely correct and grammatically sound. It is an imperative sentence, meaning it starts with a verb and issues a polite request or direct command for someone to go get water and bring it back

Rely হলো verb, Reliance হলো noun.

"I insist on your going there" is absolutely correct. It follows the standard English grammar structure of using a possessive adjective ("your") before a gerund ("going") after the preposition "on".