Give the correct form of the words: She was the first British female Prime Minister and was the longest _________ PM for over 150 years. (SERVE)

She was the first British female Prime Minister and was the longest ____serving_____ PM for over 150 years.

Dịch: Bà là nữ Thủ tướng Anh đầu tiên và là Thủ tướng phục vụ lâu nhất trong hơn 150 năm.