S1: Bananas are a good source of potassium. S2: Doctors often recommend bananas to maintain healthy levels of potassium. The second sentence:

The first sentence states that bananas are a good source of potassium. The second sentence provides supporting evidence by noting that doctors recommend bananas for maintaining potassium levels - this reinforces and validates the first statement. The second sentence confirms (affirms/supports) the assertion made in the first. Therefore, the second sentence confirms the assertion of the first.