Which of the following statements are true and which are false?

a. After you collect the data, you can then decide whether or not to use a paired design or independent samples design.
b. The simulations for paired design and independent groups design are the same. Just how the data are collected is different.
c. Paired designs can only be done in experiments and not observational studies.
d. In a paired design with repeated measures, you can use random assignment because each individual is measured twice.