Question

Le projet .............. je travaille est très difficile.

Hint:

For verbs requiring a preposition (e.g., “travailler sur”), use a relative pronoun with that preposition (e.g., “sur lequel”).

Answer 1

The verb “travailler” is used here with the preposition “sur” → “travailler sur un projet.”
When the preposition is required, we cannot use just “que” or “dont.”
We use the relative construction “sur lequel” (masculine singular to match “projet”).
Correct sentence: Le projet sur lequel je travaille est tr`es difficile.