is used is the correct answer.
Here's why:
* Passive Voice: The passive voice is used when the subject of the sentence receives the action, rather than performing it. In this case, the flour is being used.
* Forming the Passive: The passive voice is formed using a form of the verb "to be" + the past participle of the main verb.
* Present Simple: The sentence describes a general fact about cooking. Therefore, we need to use the present simple passive.
* Is used: This is the correct form of the present simple passive (is + past participle).
* Were use: This is incorrect because "flour" is singular, and "were" is used with plural subjects. Also, "use" should be the past participle "used".
* Are used: This is incorrect because "flour" is singular, and "are" is used with plural subjects.
* Is use: This is incorrect because it uses the base form of the verb "use" instead of the past participle "used".
Правильный ответ: is used