There are three kinds of Objects to be aware of:
Keys: this would be fine for the Prompt ‘Are some types of knowledge more useful than others?’ (for example) if I talk about getting my driver’s license and suddenly these are my keys as this gives them a real-life context, they exist in the world. But, keys wouldn’t be valid as symbolising keys to knowledge. Metaphors should be avoided.
Photograph of an astronaut on the moon: if a student were to choose this, they would have to make it clear that the Object they are talking about is e.g., the backpack the astronaut is wearing, or the person themselves, or the image (which is quite controversial – were men really walking on the moon?). They need to be clear.
iPhone: a phone itself will not fulfil the criteria, but an online course a student is taking on their phone would be acceptable as an Object.