By Ashitha Shivaprasad and Pablo Sinha Dec 30 (Reuters) - Platinum prices are on track for their strongest monthly rally in nearly four decades in December, fuelled ​by the EU's U-turn on its 2035 combustion-engine ban, a tight supply ‌backdrop and rising investment demand for precious metals. Platinum and palladium, both used in autocatalysts that reduce car ‌exhaust emissions, have surged this year as U.S. tariff uncertainty and a rally in gold and silver helped offset long-term headwinds from the rise ...