The constituents of automobile exhaust that can cause cancer is/are :

Car exhaust fumes contain many different things. Some of them are harmful to our health. This question asks about the parts that can cause cancer.

Option A: Oxides of nitrogen: These are gases that can irritate your lungs, but they are not directly known to cause cancer.

Option B: Carbon monoxide: This is a poisonous gas that stops your body from getting enough oxygen. It is dangerous but doesn't cause cancer directly.

Option C: Polycyclic hydrocarbons: These are a group of chemicals found in car exhaust. They are known to cause cancer.

Option D: Lead: Lead is a heavy metal, and it's toxic. While it can cause other health problems, it is not directly a known cancer-causing agent in the way polycyclic hydrocarbons are.

Therefore, the correct answer is C, Polycyclic hydrocarbons.