Which question should be asked about one pair of trousers as a plurale tantum noun denoting the single object (with two trouser legs although)?
What's this? (They're trousers.)
or
What are these? (They're trousers.)
I sometimes give English lessons and try to find a better approach to explaining the rules. Imagine a situation when a child is given a picture of trousers. The child sees one thing consisting of two parts. And I know that "trousers" is a plural noun. Which question am I supposed to ask?