Question

1.6.4 test (cst): post test: foundations of geometry
prove: if two intersecting lines form two pairs of vertical angles, one pair of angles will be acute, and one pair of angles will be obtuse.
which image provides the best counterexample for this statement?
a.
↑ ↑
↓ ↓
l m
b.
← →
↑ ↓
l m
c.
↑ ↑
↓ ↓
l m

Explanation:

A counterexample disproves the statement that intersecting lines form one acute and one obtuse vertical angle pair. Option B shows lines intersecting at right angles: all vertical angles are $90^\circ$, which are neither acute nor obtuse, violating the original claim. Option A has parallel lines (no intersection), so it does not apply. Option C forms one acute and one obtuse pair, matching the original statement.

Answer:

B. <image of lines l and m intersecting to form four right angles>