Identify the subordinate clause.
the book that i am reading concerns world population problems.
the book
the book that i am reading
book that i am reading
that i am reading
i am reading
concerns world population
this sentence contains no dependent clause

The correct answer is: that I am reading

A subordinate clause ( a dependent clause ) begins with a subordinate conjunction (as, if, than, that, where, until etc) or a relative pronoun (that, who, whom etc.) and will have a subject and a verb. This clause can not stand alone as a sentence because it does not provide a complete thought.

that I am reading is a subordinate clause because it contains a relative pronoun that introduces it ( that ), a subject ( I ) and a verb ( am reading ). It can not stand on its own because it does not have any meaning.

honestly, is this even a but since you asked, he's probably at the store trying to get you food.