The sides of similar triangles are proportional, so the ratios of corresponding sides are equal. Corresponding sides will be located opposite corresponding (congruent) angles. The measure of $\displaystyle\angle{F}\usepackage{cmbright}\Huge\$ equals the measure of $\displaystyle\angle{C}\usepackage{cmbright}\Huge\$ , so DE corresponds to AB, not to BC. The measure of $\displaystyle\angle{D}\usepackage{cmbright}\Huge\$ equals the measure of $\displaystyle\angle{A}\usepackage{cmbright}\Huge\$ , so EF corresponds to BC, not to AB.