将a²+b²+2ab=（a+b）²改写成全称命题是（　　）

A．∀a＞0，b＞0，a²+b²+2ab=（a+b）²

B．∀a，b∈R，a²+b²+2ab=（a+b）²

C．∃a＜0，b＞0，a²+b²+2ab=（a+b）²

D．∃a，b∈R，a²+b²+2ab=（a+b）²

She was certainly not afraid of the dark. ____,it was only a 15-minute ride home. [      ]

A. However

B. Besides

C. Therefore

D. Otherwise