In which of the following situations may the taxpayer take an education expense on Schedule $C?$

a$.$ Brianna, a plumber by trade, is taking classes to qualify as an electrician so she may expand her business to take on more complex contractor jobs.

b$.$ Cari, a salesperson, is flying on numerous commercial airplanes in order to observe the flight attendants so that she may improve her public relations skills.

c$.$ Harrison, a host at a restaurant, is taking a review course in order to pass the certified financial planner examination.

d$.$ Ivan, a self$-$employed administrative assistant, is taking an advanced computer skills class through an adult education program.