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? Explain.