$1-(5$ points$)$ You have been told that the following indexes are available on the Employee table on a MYSQL database:

Are you suspicious that this information is not correct. Why?

$2-(30$ points$)$ Assume in the table Employee, we have $2$ million records, and each storage page can have $20$ records. Calculate the average I$/$O cost for the following query

Select $*$ from Employee where SIN $="123-456-888"$

In following scenarios:

A$-$ We don't have any index on SIN and the database file are Heap files.

B$-$ We have B$+$ tree index on SIN, given each index page contains $100$ data entries, the file size is $1\mathrm{.}4$ of the data size, and the tree fanout is $10.$ Calculate your answer in two cases SIN wasn't primary key, and SIN was a primary Key

C$-$ We have hashing index on SIN, and SIN wasn't primary key

$3-(5$ points$)$ You are tasked with designing a database for a MUNstudent management system. The student table includes two unique columns: studentld and Email. Most queries on this table predominantly utilize studentld, while some queries use Email. Both columns are defined with a storage size of CHAR $(25).$ Your team is debating the best approach for indexing these columns. You have two options:

$-$ Set studentld as the primary key with a B$+$ tree index on email.

$-$ Set Email as the primary key with a B$+$ tree index on studentld.

Question: Which approach do you believe is better? Provide a detailed explanation of your choice, considering performance implications such as query efficiency, indexing overhead.