The observer in Thailand is located at a latitude of 60o north, which means they are in the northern hemisphere. The observer in Thailand sees Mars at an azimuth angle of 90o and an elevation angle of 45o. Based on this information, we can determine that Mars is located in the southern part of the sky. Since the question asks for the specific region, the correct answer is "ด้านตะวันออกเฉียงใต้" which translates to "southeast" in English.