What does an apple and petrol have in common ?

I was asked this question on the topic of what two different things had in common with each other by an educational psychologist while under an educational assessment for dyslexia today. It started off easy 'what does a rose and a poppy have in common ?' ''their types of flowers''. 'What does a car and boat have in common?' ''their types of transport''. Then the questions got tough after this. 'What does an apple and petrol have in common ?' ''???''. 'What does a statue and a poem have in common ?' ''??????''. 'What does a bad person and good person have in common?' ''???????''. Can someone tell me what does an apple and petrol have in common ? This has been annoying me all day.