Mixed — everything

An order is written as 900 mcg and the available solution is labeled 3 mg in each millilitre. Four setups are offered for the same problem. Which one cancels correctly to a volume before any arithmetic is done?

• A900 mcg x (1,000 mcg / 1 mg) x (1 mL / 3 mg)
• B900 mcg x (1 mg / 1,000 mcg) x (3 mg / 1 mL)
• C900 mcg x (1 mg / 1,000 mcg) x (1 mL / 3 mg)
• D900 mcg x (1 mL / 3 mg) x (1,000 mcg / 1 mg)