Fill in the blanks with the correct modal
Cancer is a potentially life-threatening illness and ______ as soon as possible.

should be treated

The correct modal to fill in the blank is should be treated. The modal should is used to express obligation or necessity, and it is the most appropriate modal to use in this context because it conveys the urgency of treating cancer. Cancer is a serious illness that can be life-threatening, so it is important to get treatment as soon as possible.

The other options are incorrect. The modal might be treated suggests that cancer may be treated, but it does not convey the same sense of urgency as should be treated. The modal can be treated is also too tentative, and it does not express the urgency of the situation. The modal could be treated is even more tentative than can be treated, and it is not used to express obligation.