Please help me to solve this sentense:
She stir fried the beef and the vegetables in a little oil.
She stir fried the beef and the vegetables with a little oil.
Welcome to the forums.
First, thank you for using correct capitalization and punctuation and for making it clear what your question was by underlining "with" and "in."
Next time, please give your thread a title that tells us about your question. Most people have a question about "Grammar" (or "vocabulary" or "usage") but we can't have all the threads with the same title. You could call this one "in/with a little oil" for example.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.