While Mendel was revising (revise) his lesson, his sister was reading (read) fables.
While Mendel was revising (revise) his lesson, his sister was reading (read) fables.
→ Hai hành động xảy ra song song → quá khứ tiếp diễn cả hai.
Dịch: Khi Mendel đang ôn bài, em gái của anh ấy đang đọc truyện ngụ ngôn.