Google, Facebook, Amazon and Apple offer defense in congressional antitrust probe

Google also said its vertical integration of advertising tools benefits advertisers in part through better consumer targeting, but that the ability of rivals to compete is not meaningfully affected because it takes steps to level the playing field.

For its part, Facebook acknowledged cutting off certain third-party apps from its developer platform for replicating core functionalities, such as Twitters now-shuttered Vine, which it said replicated a Facebook product.

For example, asked for the timing and exact circumstances that led it to remove apps Phhhoto, MessageMe, Voxer and Stackla, Facebook replied that it will restrict apps that violate its policies, without disclosing details.

Apple answered questions about its browser and commissions it pays in its App Store, and addressed other issues, most of which are generally known.

Amazon.com said in its response that it uses aggregated data from merchants on its third-party marketplace for business purposes, but denied using the data to launch, source or price private-label products.

Amazon also acknowledged asking third-party merchants to lower their price on Amazon.com, when it finds merchants sell items for less on a competing website.

Amazon declined, however, to say how many Amazon private label products are sold at cost or below cost, how much revenue and profit Amazon makes from selling private brands or how it prices such items.

Amazon said it has 45 brands encompassing 158,000 private-label products, as well as some private brand items that are part of its Amazon Fresh grocery delivery service.