interested in / interest in

The respondents expressed interest in the new product.

"The respondents" = subject of the sentence
"expressed" = transitive verb (i.e. must take on an object)
"interest in the new product" = noun phrase, the object of "expressed"

You can also replace the above noun phrase with a noun clause.
==> The respondents expressed that they were interested in the new product.

因為它時間是在過去式

因為 interest 係noun ?!

because not past test is present test