DB Chapter 347
From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
"A Sound of Thunder" (トランクスの疑惑, Torankusu no Giwaku; Literally meaning "Trunks' Confusion") is chapter 347 of the Dragon Ball manga.
Trunks wonders what's going on, and then flies off again toward the fight, thinking of how this artificial human is different from the ones he knows, wondering if there isn't three of them. No. 20 climbs up from the rubble, and can't believe Piccolo is this strong. Piccolo says they were supposed to be killed by the two artificial humans, but now the future has changed, and they've all become strong, too strong. Kuririn gets excited that they'll beat them without Goku, and Gohan agrees. Tenshinhan doesn't like the idea of Piccolo and Vegeta being so strong, but for now it's a relief. Vegeta yells at Piccolo to hurry up and finish him off, or does he want him (Vegeta) to do it. Piccolo declines, saying, "Originally, I was the incarnation of evil separated from God. I'm not naive like Goku." Then everyone stops when they feel someone coming, and when he gets close enough, Piccolo says, "Trunks!"
Vegeta thinks, "Trunks?! Trunks, he said...?! The same name... He has the same name as my brat...!! From the future... I get it...!!" Trunks looks at No. 20, and thinks that he's different too. No. 20 sees Trunks, and says he has no data on this new guy. No. 20 realizes he's made a tremendous miscalculation, and he must return to the laboratory. Trunks asks them who this is, have they been fighting him? Vegeta says it's the artificial humans he told them about. Trunks wonders what this is, and Piccolo asks if this one's different...? Meanwhile, Bulma continues flying toward them in the air car, and Yajirobe insists they go back. Bulma just wants to see that everyone's alive, and Yajirobe says if she goes any further, he'll drop this brat out the window. Bulma says go ahead, but informs him that his father is Vegeta. Yajirobe is surprised to hear that this brat, err, little darling, is her and Vegeta's son. And they continue going.
Vegeta wants to know who that is if it's not the artificial human, but Kuririn thinks maybe if history's changed a bit, then so have the artificial humans. No. 20 thinks he'll be caught if he escapes by air, so he'll just have to stealthily go by ground. Then everyone notices Bulma's air car pulling in, and Yajirobe yells that there's still a artificial human there. Bulma gets a good look at No. 20, and gets a strange expression, as Trunks yells it's dangerous, get out of here. No. 20 thinks this is his chance. "The truth is, you scum have absolutely no chance of winning!!! No. 17 and 18 will come to kill you!!!" Everyone is shocked to hear about a No. 17 and 18, and No. 20 then creates a huge explosion. Bulma's air car is caught up in the blast, but when the smoke clears, everyone is okay, and Trunks has saved Bulma and the baby Trunks. Vegeta is pissed No. 20 is gone, as Bulma thanks Trunks for saving them.
Vegeta isn't going to let him get away, but Trunks flies up in front of Vegeta, and asks him why he didn't help his wife and child. Vegeta just says that's pointless, and he has no interest in that. Bulma asks if that weird geezer was supposed to be an artificial human, then says he looked a lot like Doctor Gero. She's seen a picture of him in a scientist book before, and wonders if he didn't make himself into an artificial human, as Yajirobe climbs out of some rubble.