The correct answer is option 3: north to south. This means that summer rains in Australia generally decrease as you move from the northern regions to the southern regions.

To understand this, we can look at Australia`s climate. The northern regions, such as the tropical areas, experience a wet season during summer with heavy rainfall. As we move towards the southern regions, the rainfall decreases due to the influence of the subtropical high-pressure systems. These systems result in drier conditions in the southern parts of the country during summer.

It is important to note that this is a general trend and there can be variations due to factors like topography and seasonal weather patterns. However, as a general pattern, summer rains in Australia tend to decrease from north to south.