Answer: a) Sauce
Explanation:
Sauce is the best word to show cooking. Sauce doesn’t have many meanings, and when thought of sauce, one thinks of dishes and cooking. Sauces are mentioned mainly as a flavoring to food, which related to cooking.
Heat isn’t related directly to cooking. It can mean a hot summer, which is definitely not related to cooking.
Thicken is not either, and can be used in a sentence that doesn’t mention cooking, like the polar bear will thicken it’s coat in the winter.
And lastly, coats is not. Coats can mean jackets, and is not pictured usually as a cooking subject/thing.