Question

read the paragraph. then, add the best topic sentence.
computer programs written in the 1950s through the 1990s often represented each year with only its last two digits, like 99 instead of 1999. because the first two digits were missing, people worried that on january 1, 2000, computers would think it was 1900. many believed this would cause major computer systems around the world to fail, including those at hospitals and banks. in the end, most computer programs did not fail when the year changed from 1999 to 2000.
computers have changed a lot since they were first developed.
many people thought computer programs would fail in the year 2000.
hospitals and banks need computers to keep running.

Explanation:

The paragraph is about the Y2K problem and how computer programs (written with two - digit years) were feared to fail but most didn't. The sentence "Computers have changed a lot since they were first developed." connects the past (computer development with two - digit year programs) to the present (changes in computers that likely addressed such issues or evolved from that era), providing a good concluding thought about the evolution of computers related to the Y2K context. The other options are either too specific (talking about hospitals/banks or the fear of failure) and don't serve as a good overall closing sentence.

Answer:

Computers have changed a lot since they were first developed.