Yes. It's a little unusual in sentences which are not questions, but English is pretty flexible and it's usually possible to rearrange sentences so that, for example, they start with very nearly whatever word you want, including 'which'.
Which, if I remember properly, was your question.
The word 'is' can begin a sentence but not be a question when it is the subject of the question. Example sentence - Is can be the subject in a sentence. But only in sentences of that type (above) or, 'Is' is a two letter word. Otherwise is cannot begin a sentence.
Yes. There is no word that cannot begin an English sentence.
It is possible to have a sentence with the word it at the beginning, as this sentence proves.
Never
yes you can
Of course you can. There is no word in English that cannot begin a sentence.
Yes, you can begin a sentence with the word "or" when presenting options or alternatives. For example, "Or you can choose to study abroad for a semester."
Yes, a sentence is allowed to begin with the word "with". For example: With all the pressure of high school people were becoming stressed.
lettuce begin (let us begin)
No, You cannot use but to start a sentence.
Yes.
yes if it necessary