Company A has a contract with Company B where Company B will provide 2,000 N-95 face masks per month for Company A's employees to use during oil tank inspections.After February 2020, the supply of N-95 face masks significantly declined due to the coronavirus pandemic.Company B has been ordered by the federal government to increase supply of N-95 face masks for medical professionals, and therefore Company B cannot fulfill its obligations to Company A.Company A has lost revenue because it cannot complete oil inspections without proper protective gear.Company A has sued Company B for breach of contract.Company B's best defense would be:

mutual mistake of law

illegality

commercial impracticability

frustration of purpose