Should I use 'that' or 'which' in the following sentence?
My teaching experience and technical background are not the only factors which/that make me a suitable applicant.
Additionally, how do I know when to omit 'that' from a sentence? For instance, consider these sentences:
It was during those 2 years that I began comprehending the sophistication of techniques employed in the industry.
It was two years of my life that I enjoyed thoroughly.
I am confident that I can make a positive contribution to your organisation.
In which of the above should I omit the word and how do I know when to do so?
Thanks