underlie
/ˌʌndəˈlaɪ; ˌʌndɚ`laɪ/ v
(pt underlay / ˌʌndəˈleɪ;ˌʌndɚ`le/, pp underlain / -ˈleɪn; -`len/)
1 [I, Tn] lie or exist beneath (sth) 位於或存在於（某物）之下
the underlying clay, rock, etc 处於下层的黏土、 岩石等.
2 [Tn no passive 不用於被动语态]
(fig 比喻) form the basis of (sb's actions, a theory, etc); account for 构成（某人行动、 理论等）的基础; 作（某事物）的说明或解释
A deep faith underlies her work among refugees. 她在难民中工作是因为她有很深的信念.
the underlying reason for her refusal 她拒绝的内在原因.