An employer with 20 employees must offer COBRA continuation for

The 12-month period is not applicable under COBRA for employers with 20 or more employees. While some insurance plans may offer shorter continuation periods, COBRA specifically mandates a minimum of 18 months for continuation coverage, making this answer incorrect.

While there are provisions for extending COBRA coverage to 29 months for certain qualifying individuals, such as those who are disabled, this is not a standard requirement for all employees under COBRA. Therefore, the general rule for an employer with 20 employees is still 18 months, making this option incorrect for the general case.

The 36-month continuation period is applicable to certain beneficiaries, like dependents who lose coverage due to specific events, but it is not a standard duration for employees under COBRA. Thus, this option does not pertain to the question about the standard continuation coverage for employees, rendering it incorrect.