Which of the Following Is an Example of a Mixed

Which of the following is an example of a mixed design?

A) An investigation of the effect that an employee's gender has on the age of attaining a senior management position
B) An investigation of the effect that the gender of an accountant has on month's-end reporting errors before and after holidays
C) An investigation of the effect that the gender of an accountant has on month's-end reporting errors with and without training
D) An investigation of the effect that gender of employee's has on choice of training programme adopted.