Institution: AGRANI BANK LTD Exam: Agrani bank Ltd - Senior Officer - 12.02.2010
Topic: Preposition, Subject: English Grammar (ইংরেজি গ্রামার)

Best Answer Explained in Below-:

The phrase "hit upon" is an idiomatic expression that means to come across or discover something unexpectedly or by chance. In this context, it refers to the moment when Salam unexpectedly realizes that he has thought of an excellent idea. The use of "upon" in this phrase conveys a sense of discovery and realization, which is why it fits perfectly in the sentence.

Let's look at the other options for clarity. "Hit with" (Option A) typically suggests an impact, whether physical or metaphorical, but does not convey the notion of discovery. "Hit into" (Option B) is not commonly used in the context of ideas and would imply a collision rather than a realization. Lastly, "hit by" (Option D) also suggests being affected by something, but again lacks the meaning of discovery or insight that is conveyed by "hit upon."

Thus, the correct choice, C) upon, not only fits grammatically but also encapsulates the intended meaning of spontaneously discovering an excellent idea.