vertical angles are always \( \begin{array}{ll}\text { a) adjacent angles } & \text { () acute } \\ \text { c) total } 180 \text { degrees } & \text { d) congruent (equal measures) }\end{array} \)

Vertical angles are formed when two lines intersect. The properties of vertical angles can be summarized as follows: - Vertical angles are always **congruent**, meaning they have equal measures. Now, let's analyze the options provided: a) adjacent angles - This is incorrect because vertical angles are not adjacent; they are opposite each other. b) acute - This is not necessarily true; vertical angles can be acute, obtuse, or right angles. c) total 180 degrees - This is incorrect; while the sum of the measures of adjacent angles formed by intersecting lines is 180 degrees, vertical angles themselves are not constrained to this property. d) congruent (equal measures) - This is the correct answer. Thus, the correct answer is: **d) congruent (equal measures)**.