Understanding the Structure:

• The phrase "No sooner" is typically used to indicate that one action happens immediately after another. It sets up a cause-and-effect relationship between two events.
• In this context, "No sooner did he see us" suggests that something happened right after he saw "us."

Correct Phrase:

• The structure "No sooner... than..." is the correct idiomatic expression. It signals that the second event (the action in the clause following "than") occurs immediately after the first event.
• Therefore, "than he disappeared" is the appropriate choice because it maintains this grammatical structure and conveys that his disappearance happened right after he saw "us."
• CORRECT SENTENCE:
  
  • The phrase "No sooner did he see us than he disappeared" correctly follows the grammatical pattern and effectively communicates that his action of disappearing happened immediately after seeing us, making it the best choice.