A controversial figure throughout most of his public life, the Black leader Marcus Gaery advocated that some Blacks return to Africa, that land to him, symbolized the possibility of freedom. (1) advocate –虚拟语气的使用,省略should. (2) that land to him作为Africa的同位语,起修饰作用 为什么用symbolized而不是symbolizing来修饰that land? 会不会是symbolized前省去了which is? 如何理解?