29.立木樹高(tree height)為測計立木材積主要因子之一,我國森林調查所慣用之立木高度為何? (A)全高(total height,Ht) (B)樹冠高(crown height,Lc) (C)幹高(bole height,Hb) (D)伐根高(stump height,Hs)