Answer the following general questions about indexes:
a. Can an index be built over a non-unique field?
b. Can an index be built over a field if the file is not stored in sequence by that field?
c. Can an index be built over a combination of fields as well as over a single field?
d. Is there a limit to the number of indexes that can be built for a file?
e. How is an index affected when a change is made to a file? Does every change to a file affect every one of its indexes?
f. Can an index be used to achieve sequential access?