What grammatical structure is the italicized portion of the sentence? Houses should be designed to take advantage of the sun's heat.

a. adverb clause

b. infinitive phrase

c. past participle phrase

d. elliptical clause

e. adjective clause

In the sentence:

Houses should be designed to take advantage of the sun's heat. (guess underlined phrase: to take advantage of the sun's heat). It is an infinitive phrase. Infinitive phrases starts with infinitives that is, "to" added by a simple verb and can be used as nouns, adjectives or adverbs. In the case of including a main clause in the sentence, infinitive phrase separates it with comma