The correct response is:
Heat will flow from the block to the water until both substances have a temperature between 20 degrees Celsius and 300 degrees Celsius.
In this scenario, heat will transfer from the hotter aluminum block (initially at 300°C) to the cooler water (initially at 20°C) until thermal equilibrium is reached, meaning the two substances will settle at a final temperature that is somewhere between the initial temperatures of the block and the water.