WASHINGTON, July 29 (Xinhua) -- Top executives of Amazon, Apple, Facebook and Google on Wednesday testified virtually before the U.S. House Antitrust, Commercial, and Administrative Law Subcommittee, which hit them with tough questions over their practices.

"The purpose of today's hearing is to examine the dominance of Amazon, Apple, Facebook, and Google," David Cicilline, a Rhode Island Democrat and chairman of the subcommittee, said in his opening remarks, noting that these platforms have wielded their power "in destructive, harmful ways" in order to expand.

"Prior to the COVID-19 pandemic, these corporations already stood out as titans in our economy," Cicilline said. "In the wake of COVID-19, however, they are likely to emerge stronger and more powerful than ever before."

Representative Jerrold Nadler, a New York Democrat, pressed Facebook Founder and CEO Mark Zuckerberg on the company's purchase of Instagram, arguing that Facebook made the move to stifle competition.

The four tech executives apparently sought to dismiss such accusations, saying that they compete fairly, and also tried to downplay their market dominance in their respective fields.

Amazon Founder and CEO Jeff Bezos, for example, said in his opening remarks that Amazon accounts for less than 4 percent of retail market in the United States, and it competes against large, established players like Target, Costco, Kroger, and Walmart.

Cicilline, however, noted that Amazon operates across a vast array of businesses -- from cloud computing and movie production to transportation logistics and small business lending, and the company's market valuation recently hit 1.5 trillion U.S. dollars, more than that of Walmart, Target, Salesforce, IBM, eBay, and Etsy combined.

Apple, meanwhile, is a dominant provider of smartphones, with more than 100 million iPhone users in the United States alone, Cicilline said, adding that in addition to hardware, Apple sells services and apps, including financial services, media, and games.

The antitrust hearing came as federal and state law enforcement probes targeting Amazon, Apple, Facebook and Google have been going on and started to draw public attention.