In Option (1), "service themselves" is the correct phrase as it refers to self-service in the context of a canteen, where customers serve themselves.
In Option (2), the phrase "service lift" refers to a lift used for transporting goods, not passengers.
In Option (3), "to service the loan" correctly implies making payments or fulfilling the conditions of the loan.
In Option (4), "active service" refers to a person being actively engaged in service, such as in a job or military context.
\[
\boxed{1}
\]