Jill is a single mother with two daughters, aged $22$ and $20.$ The older daughter has been disabled since birth and will require daily medical and personal care for the rest of her life. Identify Jill's obligations to her daughters when preparing her will.

a$.$

She must ensure that both daughters receive equal portions of her estate.

b$.$

She must ensure that the will provides adequate, ongoing support for the disabled daughter, before assets are distributed to the younger daughter.$$

c$.$

She must leave the estate to the disabled daughter in a trust that will provide for the rest of that daughter's life.

d$.$

She can leave the estate to the younger daughter as long as the younger daughter has legally pledged to take care of her disabled sister.