A MySQL replication slave is set up as follows:
* Uses all InnoDB tables
* Receives ROW-based binary logs
* Has the read-only option
The replication slave has been found in an error state.
You check the MySQL error log file and find these entries:

What are two possible causes for this error to occur?

You want to immediately stop access to a database server for remote user
'mike'@'client.example.com'. This user is currently not connected to the server.
Which two actions can you take to stop any access from the user? (Choose two.)

You are asked to examine user accounts and find:

Which two statements will best secure this environment? (Choose two.)

You have successfully provisioned the latest MySQL 5.7 database instance on a physical host, to be added to an existing farm for use in a modern, high volume, ACID-compliant, OLTP website, which serves hundreds of DML transactions per second.
The default values of which two key variables do you change to ensure seamless operation of the database?
(Choose two.)

The MySQL error log shows:
InnoDB: Warning: a long semaphore wait:
The relevant parts of the InnoDB monitor output shows:

Which two options would help avoid the long wait in the future? (Choose two.)