What caused Union Carbide's deadly gas leak in Bhopal, India, which killed 3,000 and injured 42,000?

a.employees' deciding to have lunch before dealing with the pressure buildup inside the tank and bribes paid to the government employees who inspected the plant

b.diversion of funds and resources to a Northern India project that also took staff from the Bhopal plant, plus many safety issues, including fines imposed on community members who camped too close to the plant

c.a combination of low staff levels, numerous safety issues, and a lack of immediate employee attention to the problem as pressure built up inside the tank

d.a combination of low staff levels, corruption, pay-offs to employees to keep quiet, and the manager going on vacation the day before the leak