平原地区的土大都是在第四纪地质年代的下列( )阶段沉积形成的。
A <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251122/13563086_0.jpg"> B
<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251122/13563086_0_1.jpg"> C
<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251122/13563086_0_2.jpg"> D
<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251122/13563086_0_3.jpg">