The most important job of the Federal Trade Commission today is to a) prevent false and deceptive advertising b) break up unlawful trusts c) issue cease-and-desist orders when anticompetitive business practices occur d) promote commerce with foreign nations

The first step is to understand what the Federal Trade Commission is and what it does. The FTC is an independent agency of the United States government, whose primary mission is to enforce federal consumer protection laws and prevent anticompetitive business practices in the marketplace.

Next, let's examine each of the four options given in the question. a) prevent false and deceptive advertising - The FTC does have a role in preventing false and deceptive advertising by ensuring that consumers are not misled by businesses in terms of the products and services they offer. b) break up unlawful trusts - The FTC also has the authority to challenge unlawful trusts, which are agreements between businesses to manipulate the market and stifle competition. c) issue cease-and-desist orders when anticompetitive business practices occur - This is another function of the FTC, where it can issue orders to businesses to stop engaging in practices that harm competition in the marketplace. d) promote commerce with foreign nations - Although the FTC does have some role in facilitating international collaboration, it is not their primary focus.

Based on our understanding of the FTC and the various roles it plays, it seems that the most critical function the agency currently performs is to prevent false and deceptive advertising, as it has a direct impact on protecting consumers and ensuring a fair marketplace. So, the correct answer is: a) prevent false and deceptive advertising