U

Infinitive

（动词原形）

Simple  Past

（过去分词）

Past  Participle

（完成分词）

unbend   

straighten up or out;  make straight

松弛，弄直

unbent

unbent

unbind

untie or unfasten

解开

unbound

unbound

unclothe

get undressed

脱去衣服

unclothed / unclad 

unclothed / unclad 

underbid

bid lower than a competing bidder

喊价过低

underbid

underbid

undercut

sell cheaper than one's competition

廉价出售，削弱

undercut

undercut

underfeed

不给足量食物

underfed

underfed

undergo

go through

经受

underwent

undergone

underlie

be or form the base for

位于…之下

underlay

underlain

undersell

sell cheaper than one's competition

以低于市价售出

undersold

undersold

underspend

spend less than the whole of (a budget, for  example)

花费少

underspent

underspent

understand

know and comprehend the nature or meaning of

理解

understood

understood

undertake

enter upon an activity or enterprise

从事

undertook

undertaken

underwrite

guarantee financial support of

认购，为…保险

underwrote

underwritten

undo

cancel,  annul, or reverse an action or its effect

解开，废除

undid

undone

unwind

reverse the winding or twisting of

解开

unwound

unwound

uphold

keep or maintain in unaltered condition; cause to remain or last

·          preserve the peace in the family

鼓励，支持

upheld

upheld

upset

afflicted with or marked by anxious  uneasiness or trouble or grief

心烦的

upset

upset