A. Go to File > Options > Formulas > Calculation Option - and mark the corresponding radio button
B. both
C. Double CAL indicator on status bar
D. none
Explanation
When you press F9 or click Calc Sheet on the Calculation tab on the Tools/Options menu.
Calculation also occurs every time that you save the file if you have the checkbox "Recalculate workbook before saving" checked under File > Options > Formulas.