Some stores are testing a new checkout system that allows
shoppers to use their mobile phones to scan items as they
walk through stores and pay at self-service kiosks, skipping
the cashiers’ lines.
the new mobile checkout system reduces long lines and
customer wait times in stores.
what does the second sentence do?
a. it expands on the first.
b. it states an effect.
c. it contrasts with the first.
d. it gives an example.

- "a nonrestrictive clause functions as a modifier to a noun (that is an object, person or concept). these clauses can be described by the following three options: it is set off by comas, it contains a subject and a verbs and it adds nonessential information to the sentence.

for example, in "here is bill gates, who confounded microsoft software company" we can identify "who confounded microsoft software company" as a nonrestrictive clause modifying the noun bill gates. this clause can be describes as a nonrestrictive clause because it is separated by a comma, it adds nonessential information to identify who bill gates is and it must contain both a subject (who) and a verb (confounded)."