An isosceles triangle has at least two equal sides. The base angles opposite the equal sides are also equal.<br><br>
&bull; All 3 sides equal &mdash; this is equilateral, not the defining feature of isosceles.<br>
&bull; All 3 angles the same &mdash; this describes equilateral, not all isosceles triangles.<br>
&bull; 2 angles must be equal &mdash; TRUE. The base angles of an isosceles triangle are equal.<br>
&bull; All 3 angles different &mdash; FALSE (a scalene triangle).<br>
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Final Answer: C: 2 angles must be equal