Hi
For others reading this thread, the plagiarism rules are set out here (as of April 2021 - this may change in future).
The key text in relation to your specific question is this:
Where a question is asking for content such as definitions or listing principles which the IFoA recognises you may have memorised, you will not generally be investigated for plagiarism where such similarity is identified. In answering other question types, if your response includes quotations, theories, ideas, data or any other materials which are the work of another person or persons, you must ensure that you have taken all reasonable steps to acknowledge the source. This includes all text books, study materials and internet sources.
This recognises that reproducing definitions or principles (which is the sort of thing that might come up in the CM, CB and CS exams) falls outside of the definition of plagiarism, and therefore it is not necessary to reference it.
This is much more of an issue in the later exams, where long form discussion questions are more common, and ideas are explored more deeply.
CB2 is unusual among the early exams in that it does have long answer wordy questions. In this case you need to ensure that what you are submitting is your own work, and not a reproduction or paraphrasing of another source. A well-prepared candidate should be able to distil the key ideas into an answer without direct or approximate quotation.
Dave