A 90-minute “Frontline” (8 p.m., PBS, check local listings) examines one of the most powerful images of recent times. “The Tank Man” recalls the student and worker protests in China’s Tiananmen Square in early June 1989. For a few days, it seemed that a new breed of people power would topple the Communist government that had ruled with Stalinist ruthlessness for 40 years. Instead, the regime sent in troops and tanks. Thousands were killed, and the demonstrators were dispersed. Days later, a lone man, thought to be a worker, stood alone in front of a line of tanks. Defiant, alone, defenseless – he became a living symbol of individual resistance.

But what happened to the anonymous “Tank Man,” and what has happened to China since Tiananmen Square?

“Frontline” interviews journalists and human-rights activists who have heard rumors about his arrest and possible execution over the years. They also explain how China’s repressive regime has used the nation’s explosive economic growth as a kind of safety valve against dissent.

When “Frontline” reporters showed current Chinese university students a picture of the “Tank Man,” they had no idea who he was. Memory of his resistance had been all but vaporized in his native land.

Rapid change has brought prosperity for some but dire conditions for more than a billion Chinese. Most cannot afford newly privatized medical care and education, and pressures for change are mounting. Last year, there were more than 70,000 demonstrations, many of them violent, but few have been covered by the news media.

Most chilling of all, this “Frontline” explains why American corporations, including Google, Yahoo! and Cisco Systems, have cooperated with Chinese authorities to censor news and information and to help them locate alleged “subversives.”

¢ The ghosts of accident victims confront our heroine on “Veronica Mars” (8 p.m., UPN). “Mars” will air at this time for the remainder of this season.

Tonight’s other highlights

¢ “Protocols of Zion” (6 p.m., Cinemax) examines the enduring influence and infamy of a fraudulent “report” concocted in 1905 to whip up anti-Semitic hysteria in czarist Russia.

¢ Two Marine wives are found slain on “NCIS” (7 p.m., CBS).

¢ The remaining contestants take on the music of Queen on “American Idol” (7 p.m., Fox). What’s next, Electric Light Orchestra?

¢ Linus explains another curious holiday tradition in the 1994 animated special “It’s the Easter Beagle, Charlie Brown” (7 p.m., ABC).

¢ If you can’t beat “American Idol,” you might as well join it. Paul Anka guest stars on “Gilmore Girls” (7 p.m., WB).

¢ A mission to bug an embassy hits unforeseen snags on “The Unit” (8 p.m., CBS).

¢ A patient exhibits identical symptoms to a boy who recently died on “House” (8 p.m., Fox).

¢ The pharaoh’s army gets in a little over its head as “The Ten Commandments” (8 p.m., ABC) concludes.

¢ Two killings, one suspect on “CSI” (9 p.m., CBS).