In this contract asks me to pay 3000 dollars and a person who guarantee when I do not pay back the money.
I have some uncertainities about the contract. I want to ask you about the two points.
first question: what do you call a person who guarantee when I do not pay back the money.
second question: Is uncertainity pluralized because there are two places I'm uncertain.
2. the plural 'uncertainties' is best used in a very general sense, as in 'the uncertainties of life', rather than 'two/three/a number of uncertainties'.
It is better to phrase it:
"I am/I'm uncertain about something (that you said)."
"I am/I'm uncertain about a couple of things..."
"I have/There are a number of things I am still uncertain about." (and then you go on to talk about them).