Topic: Word Meaning, Subject: English Grammar (ইংরেজি গ্রামার)

Best Answer Explained in Below-:

The phrase "at one's fingertips" refers to having complete knowledge or immediate access to information. It suggests that the relevant knowledge or skills are readily available, just like how you can quickly use your fingers to retrieve an item or perform a task. This idiom often implies that someone is well-prepared or knowledgeable in a particular area, allowing them to respond promptly and effectively to questions or challenges.

For example, a professional who has all the necessary guidelines and data readily accessible would be said to have that information "at their fingertips," enabling them to make informed decisions quickly. In contrast, the other options do not align with the intuitive meaning of the phrase. "To take revenge" (A) and "matter of shame" (B) relate to emotional or social concepts, while "injured finger" (D) is a literal and physical interpretation that strays far from the idiomatic sense. Therefore, "complete knowledge" (C) captures the essence of being thoroughly informed and prepared, making it the correct answer.