Agriculture is the largest user of Colorado River water, accounting for about 70–80% of its withdrawals, primarily for irrigation in states like California and Arizona. Option B (agriculture) is correct. The APA’sAICP Certification Exam Content Outline(2022), under “Areas of Practice,” notes, “Agriculture is the dominant user of Colorado River water, far exceeding other sectors like housing or industry.” Option A (oil and gas) and C (industrial) use significantly less water. Option D (housing) accounts for a smaller share, mainly for municipal use. TheCPC Study Manual(2024) confirms, “Agriculture uses the majority of Colorado River water, supporting irrigation in the Southwest,” supporting option B.