While auscultating heart sounds of a client with heart failure, the nurse hears an extra heart sound immediately after the second heart sound (S₂). The nurse should document this as

A. a first heart sound (S₁).
B. a third heart sound (S₃).
C. a fourth heart sound (S₄).
D. a murmur.

地面上无论大圆或小圆在投影中的表象仍为一个圆的地图投影是（）。

A.彭纳投影

B.球心投影

C.墨卡托投影

D.球面投影