A right-angled triangle has exactly one 90&deg; angle. The other two angles are acute and sum to 90&deg;.<br><br>
&bull; All sides same &mdash; FALSE (that is equilateral, angles would be 60&deg;).<br>
&bull; All sides different &mdash; not necessarily true (a right isosceles triangle has two equal sides).<br>
&bull; 1 and only 1 angle is 90&deg; &mdash; TRUE. A triangle can have only one right angle (sum of angles = 180&deg;).<br>
&bull; All 3 angles different &mdash; not necessarily (a right isosceles triangle has 45&deg;, 45&deg;, 90&deg;).<br>
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Final Answer: C: 1 and only 1 angle is 90 degrees