Both assertion (A) and reason (R) are true. The continents do develop low pressure in summers compared to the oceans. This is because the continents tend to be relatively warmer during the summer months. The reason for this is that land absorbs and retains heat from the sun more efficiently than water does. As a result, during the summer, the land on the continents heats up more quickly and to higher temperatures than the ocean waters.

This temperature difference between the land and the sea creates a pressure difference as warm air rises over the continents, creating a low-pressure system. In contrast, the cooler ocean waters create a higher pressure system. These pressure differences then lead to the development of winds, with air flowing from the higher pressure system over the oceans towards the lower pressure system over the continents.

Therefore, reason (R) is the correct explanation of assertion (A). The relatively warmer temperatures on the continents in summers cause the development of low pressure systems compared to the oceans.