There is no doubt that doing sit-ups is the most effective way to exercise abdominal muscles.

A、毫无疑问仰卧起坐最能锻炼腹部肌肉。

B、毫无疑问仰卧起坐是锻炼腹部肌肉最有效的方法。

C、仰卧起坐最能锻炼腹部肌肉是毫无疑问的事。

---