Final answer:
The client's response that variant angina is less predictable and a precursor of MI indicates effective teaching.
Step-by-step explanation:
To determine if the teaching on variant angina has been effective, we need to identify a statement that accurately reflects the information provided by the nurse. Variant angina is also known as Prinzmetal's angina and is characterized by angina that occurs at rest due to coronary artery vasospasms. This type of angina is less predictable and is not necessarily induced by exercise or occur at the same time each day. Option D, 'Less predictable and a precursor of MI,' accurately reflects the teaching on variant angina, indicating that the teaching has been effective.