Question

All verb tenses are formed using the _____..

Answer 1

The questions is asking to state or complete the said passage in your post, base on my research and further investigation, I would say that the answer would be that All verb tenses are formed using the infinitive verb. I hope you are satisfied with my answer and feel free to ask for more

Answer 2

All verb tenses are formed using principal parts. This basically means the main verb because you have tenses like present simple, where there is only the principal part like He runs, while there are also tenses like present perfect, which is built from auxiliary/helping verb + principal part such as He has read that book before, where “has” is an auxiliary verb and read is the principal part