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An Intrauterine Device (IUD) is primarily used for contraception, and the correct answer focuses on one of its key mechanisms of action, which is to release hormones that thicken cervical mucus. This thickened mucus acts as a barrier to sperm, making it more difficult for them to enter the uterus and fertilize an egg.

In hormone-releasing IUDs, the hormone levonorgestrel is often released, which not only thickens the cervical mucus but can also inhibit sperm movement and function, further reducing the likelihood of fertilization. Additionally, this hormone can have effects on the endometrium (the lining of the uterus), making it less conducive for a fertilized egg to implant, although the central mechanism highlighted in the correct answer revolves around cervical mucus.

Other options, while related to contraception, describe different methods or mechanisms of action. For instance, preventing sperm entry relates more directly to barriers such as condoms or certain non-hormonal IUDs, delivering hormones is a function of some contraceptive implants or hormone pills, and preventing egg release refers to the action of methods like birth control pills, which primarily work by suppressing ovulation rather than through the specific function of an IUD. Thus, the focus