I won't try acupuncture _________________ my doctor's approval for the idea.

The choice "unless I receive" is the correct answer because it accurately conveys the conditional nature of the statement regarding acupuncture. The phrase indicates that the speaker will not attempt acupuncture at all unless they have received their doctor's approval. This highlights the dependency on the doctor's approval as a necessary condition for proceeding with acupuncture.

In this context, the use of "unless" sets up a clear scenario where the action of trying acupuncture is contingent upon obtaining approval. Therefore, without that approval, the action will not take place.

Other phrases do not fit as well with the intended meaning. For instance, "if I receive" suggests that the speaker might consider acupuncture only after receiving approval, which subtly changes the implication. "Despite my doctor's approval" contradicts the premise completely, implying that the speaker would still go ahead with acupuncture regardless of the doctor's opinion, which is not aligned with the intent of the original statement. Lastly, "when I get" introduces a sense of inevitability regarding the approval, suggesting it is only a matter of time before they proceed, rather than tying the action directly to the approval. Thus, "unless I receive" is the most precise and effective way to convey the speaker's condition for trying acupuncture.