In others, they may be optional for an additional cost.

Kindergarten is optional for children between 3 and 6 years old.

Suffering is usually optional for those of us fortunate enough to live in 1st world countries.

One of these courses is optional for students in grade 8.

It is completely optional for you to participate in these programs.

Furthermore, live music became optional for the first time in the Contest's history.

These courses are optional for all members of the faith.

Boys of the school must wear ties, but this is optional for girls.

Air conditioning and power windows are optional for this car.

Side air bags are optional for the first time this year.