branch : 普通用词，泛指树木比bough小一些的大枝或小枝，也可用于引申意义。
- bare/leafy/flowering branches
- The fruit on the lower branches was protected from the sun.
- Watch out for overhanging branches.
limb : 多指主枝或大枝。
- An 18-year-old student at California State University died yesterday when she was struck by a falling limb from a large oak tree.
bough : 指主枝或粗大强壮的枝。
- I rested my fishing rod against a pine bough.
shoot : 指植物或灌木刚长出的新枝、嫩枝或嫩芽。
- Two weeks after we'd planted the seeds, little green shoots started to appear.
- The first green shoots (= hopeful signs) of economic recovery have started to appear.