Brianna: It would have been better to buy a tree last summer rather than this summer. The one we bought this summer is struggling to survive this summer' s drought. If we had bought one last summer, it would have been able to survive this summer' s drought, because last summer' s normal rainfall would have enabled it to develop established roots. Trees with established roots can better withstand droughts. Which one of the following most accurately expresses the overall conclusion drawn in Brianna's argument? ['Trees with established roots can better withstand droughts.', 'It would have been better to buy a tree last summer rather than this summer.', "If a tree had been purchased last summer, it would be better able to survive this summer's drought.", "The tree purchased this summer is struggling to survive this summer's drought."]