Which of the following is true?

A random walk for stock price changes is inconsistent with observed patterns in price changes.

If the stock market follows a random walk, price changes should be highly correlated.

If the stock market is weak form efficient, then stock prices follow a random walk.

All of these.

Both If the stock market follows a random walk, price changes should be highly correlated; and If the stock market is weak form efficient, then stock prices follow a random walk.