it is not possible because estar is temporary so there is no way that you can
You use the past tense form which is 'had'.
Is can be used in the past tense if it's in its past tense form, which is was.
"is' is present tense. For past tense use was or were.
I used the past tense to answer this question.
The past tense is involved.
'Who' is a pronoun, it doesn't have a past tense. But you can use the word "was" as in "who was on the phone?".
No. The word "are" is present or future tense. The past tense would be "were".
Would is the past tense for will
This is the conditional tense. For "ser" it is "sería", and for "estar" it is "estaría". The one you use depends on context.
No, the past tense is always put.
'Conference' is a noun, it doesn't have a past tense.
is - is present tense. He is from China. was - is past tense. He was sick last week.