Which words in the sentence are the complete infinitive phrase?

Because she had never baked a cake before, Sharon decided to follow the recipe carefully.

a. because she had

b. Sharon decided to follow

c. baked a cake before

d. to follow the recipe carefully

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. In the sentence:Because she had never baked a cake before, Sharon decided to follow the recipe carefully. A main clause is put first ‘Because she had never baked a cake before’ then a comma is added, so that means the infinitive phrase is ‘d. to follow the recipe carefully’.