Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Version | Release date | Distribution mechanism | Features | Security issues |
| --- | --- | --- | --- | --- |
| 1.5a | September 1997–March 1998 | Microsoft website | Service release | 99-025 |
| 1.5b | September 1997–March 1998 | Windows NT 4.0 Option Pack Microsoft Office 97 | Service release | 99-025 |
| 2.0SP1 | July 1, 1998 | Windows NT 4.0 SP4 | Y2K remediation for Windows NT 4.0 | 98-004 |
| 2.0SP2 | July 1, 1998 | Microsoft website | Y2K remediation for all platforms | 98-004 |
| 2.8 | August 2003 | Windows Server 2003 Microsoft website | Fixed bugs and security issues | 03-033 04-003 |
Question:
If the version is 1.5b, what is the distribution mechanism?
Answer:
Windows NT 4.0 Option Pack Microsoft Office 97