— ___________________

— Once or twice a week.

A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.

精神发育迟滞是指起病于____岁以前．智商低于____，有不同程度的____困难，根据其严重程度可分为4级，各级IQ为轻度____、中度____、重度____和极重度____。