ExplanationGiven RST is an isosceles triangle and one measure of angle \(= 40\) degrees

It could be that another angle also measures 40 degrees and the third angle of the triangle measures \(100\) degrees as sum of angles in a triangle add to \(180\)degrees

Or, It could be the case that one angle is \(40\) and the remaining \(140\) degree is equally divided among the two angles of \(70\) degree each

Hence sum of two angles could be \(40 + 40 =80\) or \(70 + 70 = 140\)

Therefore sum of angles of RST could either be greater than or smaller than 120

Hence D

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This is my response to the question and may be incorrect. Feel free to rectify any mistakes