59.如【圖 59】所示之連桿機構，在此平衡位置 θ，當使用虛功原理時，P 施力所作之虛功為何？ (A)-3Psinθδθ (B) -3Psinθδθ (C)-3Pcosθδθ (D)+3Pcosθδθ

5. The cholesterol associated with animal cell membranes (A) is attached to membrane proteins and extends into the watery environment surrounding the cell. (B) helps to keep phospholipids from being too close to one another. (C) is an abnormality resulting from a diet high in cholesterol. (D) helps solidify the membranes when the room temperature is below freezing.