The road(主语) is covered with(谓语) snow(宾语).I(主语) can not understand(谓语) why they insist on going by motorbike(从句作宾语).
why(状语) they(主语) insist on(谓语) going by motorbike(动名词作宾语)
————【译苦思甜】团队成员回答