gratuitous adj.无理由的
Her gratuitous performance is not expected by the producer
source n.来源，源头(beginning origin)
account n.原因
On no account can we ignore the value of knowledge
reason n.原因 v.推论(deduce)
sake n.缘故 原因(reason)
He would do anything for money's sake
cause vt.导致 n.原因(reason)
The heavy rain was the cause of the flood
impute vt.归咎于(ascribe,attribute)
I impute his failure to laziness
attribute vt.归因于(accredit ascribe)
The discovery of electricity is attributed to Benjamin Franklin.