11当车辆触发几个传感器时判为单胎（）。
A.小于2个
B.小于等于2个
C.小于等于3个
D.4个
参考答案：C
因山顶有湖，芦苇茂密，结草为荡，南归秋雁多宿于此，故名雁荡山。
The old man didn’t have a rest ______ his son came back..
A. after B. until C. when
