Final answer:
A contact hour as defined by TAC 157.38(d) refers to 50 minutes of instruction, which is not represented by any of the provided options in the question.
Step-by-step explanation:
Per the TAC 157.38(d) definitions, which are related to Continuing Education, a contact hour is defined as 50 minutes of actual instruction time. Therefore, none of the provided options (a. 30 minutes, b. 45 minutes, c. 60 minutes, d. 90 minutes) accurately reflect the definition of a contact hour as specified in the TAC regulations. Standardly, a contact hour often encompasses 60 minutes of instruction in many educational settings, but under TAC 157.38(d), it is unique in specifying a shorter duration of 50 minutes.