Which of the following statements is/are true when two straight lines intersect? I. Adjacent angles are equal II. Vertically opposite angles are equal III. ...

When two straight lines intersect, they form four angles at the point of intersection. - Vertically opposite angles are opposite to each other and are equal in measure. This is true and corresponds to statement II. - Adjacent angles are two angles that share a common vertex and a common side. They are not necessarily equal, but their sum is equal to 180 degrees. This is true and corresponds to statement III. - Statement I is not true because adjacent angles need not be equal in measure. For example, two adjacent angles in a scalene triangle are not equal in measure. Therefore, the correct answer is II and III only.