How many rules are needed at the very least before a system in two unknowns can have a single solution?

1. A single rule in two unknowns is satisfied by every point along a whole line, so it pins down nothing on its own. 2. A second rule is needed to cut that line down to a single point. 3. In general there must be at least as many rules as there are unknowns. 4. Even that does not guarantee one answer, since two rules may give a parallel pair or the same line twice. 5. So option B states the requirement correctly while option A stops one rule short. _Source: OpenStax College Algebra (CC BY 4.0), Ch 7 "Systems of Equations and Inequalities", section 7.1 Systems of Linear Equations: Two Variables_