What index measures the overall value of ASX-listed companies?

The All Ordinaries Index (AOI) is the correct answer because it specifically measures the performance of the largest and most actively traded companies listed on the Australian Securities Exchange (ASX). This index represents the overall value of ASX-listed companies and provides a benchmark for the Australian stock market's overall performance, reflecting changes in market capitalization of these companies.

In contrast, the other options refer to indexes that are specific to other countries. The Dow Jones Industrial Average tracks 30 major companies in the United States, the NASDAQ Composite focuses on technology and biotech companies listed on the NASDAQ exchange in the U.S., and the FTSE 100 Index comprises the largest companies listed on the London Stock Exchange. Therefore, they do not measure the value of ASX-listed companies, making the All Ordinaries Index the appropriate choice for this question.