Answer: The right answer is "by recounting the events as they happened."
Explanation: The use of the pronoun "I" makes the narration more personal and arguably more engaging, but it does not necessarily build suspense. In addition, Miep Gies is not providing the reader with detailed information about the office or the time of the day - quite the opposite, she is being rather sparing in her description. However, she is recounting the events as they happened, chronologically, and she is doing it in an almost telegraphic way, using short sentences with just the necessary, unambiguous, words, and using direct speech to quote the exact words that were spoken by the man with the gun.