Identify the missing word(s) in the following sentence within the context of Microsoft Azure. The Key Phrase Extraction feature is useful if you need to quickly identify the main points in a collection of documents. For example, given input text " The food was delicious and the staff was wonderful ", the service returns the main topics: " food " and " wonderful staff ". The Key Phrase Extraction API evaluates [ ? ] text and returns a list of key phrases. Key phrase extraction is useful if you need to quickly identify the main points in a collection of documents.