峡谷
参考答案：
横剖面呈明显V字型，有时呈谷中谷现象，谷坡陡峭，坡上有阶状陡坎。谷底出现岩滩和沙砾滩，后者不稳定。
Jerry promised that he would be back ____ 2 o'clock while Rodman promised that he would turn up ____
2 hours. [ ]
A. after; after
B. after; in
C. at; after
D. in; in
PR间期固定，P波后均有QRS波， PR间期＞0.20秒见于
A．第一度房室传导阻滞 B．第二度Ⅰ型房室传导阻滞 C．第二度Ⅱ型房室传导阻滞 D．第三度房室传导阻滞 E．室内传导阻滞
