Which of the following scenarios may lead to an irrecoverable

Which of the following scenarios may lead to an irrecoverable error in a database system?

1. A transaction writes a data item after it is read by an uncommitted transaction
2. A transaction reads a data item after it is read by an uncommitted transaction
3. A transaction reads a data item after it is written by a committed transaction
4. A transaction reads a data item after it is written by an uncommitted transaction

A transaction reads a data item after it is written by an uncommitted transaction. As the errors cannot recovered in this situation.