1. be obliged to 有责任/义务做某事
It seems he has no ability to raise himself, but he never thinks he is obliged to do so.
他似乎没有能力养活自己的能力，但他也从来不认为自己有责任这么做um;.nTgT9YnfG*c-p。

2. play a pivotal role in 发挥关键作用
Despite its resurgence, few believe the party will play a pivotal role in national politics.
尽管日共正在复苏，然而极少有人相信该党会在国内政治中起到中坚作用8&&7lzW,!yQB。

3. pose a challenge for sb.构成挑战
A 10 is a book that might even pose a challenge for us, and a 4 is probably around the easiest book we would recommend.
一本难度为10的书即使对我们而言也是一个挑战，而一本难度为4的大概是我们推荐的书中最容易的T6bR&#[LHC-。

4. rely disproportionately on 严重依赖于
People with HIV/AIDS rely disproportionately on the public sector for their health care, particularly Medicaid.
艾滋病患者的医疗保健严重依赖公共部门，尤其是医疗补助计划6CKe]~EHM.b#Y6。