Question on Sponsoring a Student Dependent

[9elizabeth]

Hi,
I found an employee who is a student dependent at the moment who is willing to work for us and we agreed to sponsor him.
I am about to fill in CoS. While filling Create and Assign CoS, it is asking me to choose one of the following categories:
1) Skilled Worker (Switching immigration category - ISC Liable)
2) Skilled Worker (Extension - ISC Exempt)
3) Skilled Worker (Extension - ISC Liable)
4) Skilled Worker (Changes of Employment - ISC Exempt)
5) Skilled Worker (Changes of Employment - ISC Liable)
6) Skilled Worker (graduate in Tier 4/Student Route switching to Skilled Worker)
7) 1) Skilled Worker (Switching immigration category - ISC Exampt)

Can you please suggest me which of the above should I choose?
Your earliest reply is highly appreciated.

[9elizabeth]

Waiting to hear from you guys..!