Whileworkinginthecountryside,thestudentsagreatdealofknowledgeonplantlife.
A.looked upB.picked upC.put upD.called up在线课程B
解析：
词义辨析。looked up抬头看，查找；
picked up学会；
put up挂起，张贴；
called up给某人打电话。句意：在农村工作时，学生们选学会了大量关于植物的知识。所以选B。