A client with type 1 (insulin-dependent) diabetes mellitus has just learned she’s pregnant. The nurse is teaching her about insulin requirements during pregnancy. Which guideline should the nurse provide（）
A. "Insulin requirements don’t change during pregnancy. Continue your current regimen. "
B. "Insulin requirements usually decrease during the last two trimesters. "
C. "Insulin requirements usually decrease during the first trimester. "
D. "Insulin requirements increase greatly during labor. "
