__ the beginning of his career,Thomas Edison mostly invented telegraphic devices. Bbl6epuTe ORMH OTBeT: a. At b. . In

The correct answer is b. "In".<br /><br />The sentence should read: "In the beginning of his career, Thomas Edison mostly invented telegraphic devices."<br /><br />The preposition "in" is used to indicate a specific time period or phase, such as the beginning of someone's career.