问题补充：
The parents are by law to send their children to school.
A. demanded
B. required
C. requested
D. called
答案：
A. demanded
(答案→)B. required
C. requested
D. called
解析：考查动词辨析。require是及物动词，指正式的“要求，命令”希望得到遵守；request也是及物动词，要求，请求，语气较弱。Demand需求，查询，语气相对严肃、强烈。Call呼叫，召集。句意：法律要求父母必须送孩子去上学。故选B。
