如图所示,轻绳AB能承受的最大拉力为100N,在它下面悬挂一重为50N的重物,分两种情况缓慢地拉起重物。第一次,施加一水平方向的力F作用于轻绳AB的O点;第二次用拴有光滑小环的绳子,且绳子所能承受的最大拉力也为50N。绳子刚好断裂时,绳AB上部分与竖直方向的夹角分别为和,关于两者大小关系的说法中正确的是( ) A . > B . = C . < D . 无法确定 The new books are of great use. They ____ well and ____ already.A. sell; sell out B. sold; had sold outC. sold; have sold out D. sell; have been sold out