( ( To ( ( ( reverse ( the ( sort order ) ) ) , ) ( click ( ( the arrow ) ( in ( the column ) ) ) ) ) ) ( ( head again ) . ) )
(ROOT (S (S (VP (TO To) (VP (VP (VB reverse) (NP (DT the) (NN sort) (NN order))) (, ,) (VP (VB click) (NP (NP (DT the) (NN arrow)) (PP (IN in) (NP (DT the) (NN column)))))))) (VP (VBP head) (ADVP (RB again))) (. .)))
To reverse the sort order, click the arrow in the column head again.
(ROOT (S (NP (JJ Reversible) (NNS reactions)) (VP (VBP are) (VP (VBN indicated) (PP (IN by) (NP (NP (JJ opposite-headed) (NNS kinds)) (PP (IN of) (NP (NNS arrows))))))) (. .)))
Reversible reactions are indicated by opposite-headed kinds of arrows.