The FTC controls on product comparisons: a. no longer exist. b. are a high regulatory priority. c. are very stringent. d. have changed dramatically with private enforcement.

D

Have changed dramatically with private enforcement

Explanation:

The Federal trade commission (FTC) is an independent agency of the United States government. It's principal responsibility is to enforce the provisions of the Federal Trade Commission Act, which prohibits "unfair or deceptive acts or practices in commerce." FTC permits and even encourages product comparisons, but such comparisons must be accurate so as not to confuse the populace.

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.