IBM was ___ the world's largest supplier of computer chips and software, but now Intel and Microsoft have taken its place.
Looking at the full text of the question and the options shown in the image in the comments, I would say the correct answer to the question is actually A: bound for.
See definition #1 of bound from dictionary.com:
- going or intending to go; on the way to; destined (usually followed by for)
A few decades ago, IBM was one of the biggest companies in the computing industry. The sentence tell us that IBM was so big, in fact, that it was on its way to being the world's largest supplier of computer chips and software. But over time, both Microsoft and Intel outpaced IBM in growth. Intel became an industry leader in chipmaking, and Microsoft became an industry leader in software. That left IBM farther back in the pack of the industry, where they have remained to this day – still a large, successful company, but no longer growing so quickly as to be on their way to becoming a world leader in either category. (I'm not sure IBM even makes computer chips or software these days, actually.)