<Li> Energy <Ul> <Li> Petroleum </Li> <Li> Electricity </Li> </Ul> </Li> <Ul> <Li> Petroleum </Li> <Li> Electricity </Li> </Ul> <Dl> <Dt> Secondary sector </Dt> <Dd> <Ul> <Li> Automotives </Li> <Li> Aerospace </Li> </Ul> </Dd> </Dl> <Dd> <Ul> <Li> Automotives </Li> <Li> Aerospace </Li> </Ul> </Dd>

What industry has been essential to canada's economic development