What technique does the author use to tell us about sergei’s wishes of this goldfish what would you wish?

Incomplete question. Here's the excerpt,

"That first wish, Sergei used up when they discovered cancer in his sister. A lung cancer, the kind you don’t get better from. The fish undid it in an instant—the words barely out of Sergei’s mouth. The second wish Sergei used up five years ago, on Sveta’s boy. The kid was still small then, barely three, but the doctors already knew something in her son’s head wasn’t right. He was going to grow big but not in the brain. Three was about as smart as he’d get. Sveta cried to Sergei in bed all night. Sergei walked home along the beach when the sun came up, and he called to the fish, asked the goldfish to fix it as soon as he’d crossed through the door. He never told Sveta".

flashback technique

Explanation:

Note, a flashback in a story involves a mental reflection about an event or scene that had taken place in the past and is then mentioned in the present time in a chronological and appealing way.

Thus, we could notice how that Sergei's previous wishes are recalled by the author so the reader thinks back to earlier times.

what are the sentences?

one is a red flower, and one is the sky when the sun sets.