A It’s a common use of the hyphen to connect different parts of the speech as one noun.

B Because compound nouns require hyphens.

C Whenever there is a word combination with a gerund or infinitive form, the hyphen is mandatory.

D Because they are two-word adjectives (or nouns and participles working as adjectives) united by the hyphen to describe the same object.

E The hyphen is optional in the three sentences, and it was used to preserve a more formal writing style.