Jane
Thickening agents like cornstarch are used to create a sauce that will coat the ingredients- you can reduce the sauce by simmering it down, and get a similar effect, or use an ingredient like arrowroot or guar gum.
Rice wine and rice wine vinegar are a traditional ingredient, to create that balance between sweet and sour.You could try using lemon juice to get a similar effect- it won't taste quite authentic but taste and find the balance you like. A dash of dry white wine will help if you're happy to use that..
ramit
Because the people in china are bitter in talking so they dont need any venegar .