"Look-alike drugs" is the term used to describe nonprescription drugs that look like narcotic drugs and are sold on the streets as narcotic drugs. After extensive hearings, Congress concluded that the sale of look-alike drugs was widespread in this country and was creating severe health and law enforcement problems. To combat these problems, Congress enacted a comprehensive statute that regulates the manufacture, distribution, and sale of all nonprescription drugs in the United States. Which of the following sources of constitutional authority can most easily be used to justify the authority of Congress to enact this statute? 
The spending power. The commerce clause. The general welfare clause. The enforcement powers of the Fourteenth Amendment.