Final answer:
The infinitive phrases are 'to measure' in option A and 'to work' in option D. These phrases start with the word 'to' which is a way to identify infinite phrases followed by a verb and serve a specific function in the sentence.
Step-by-step explanation:
The infinitive phrases in the given options are:
- A. It is important to measure all ingredients by weight when you bake.
- D. To work in a professional kitchen, it is necessary to learn about food safety.
These phrases include the word 'to' followed by a verb forming the infinitive, and they act as a noun or modifier within the sentence, providing additional context or expressing purpose.