Could you please help me with these sentences? Which would you say? How would you say them please?

- I can smell it even with your mouth closed/when your mouth is closed.
- I'd hate to be the person whose car that belongs to/whose car that is.
- I keeping having/running into problems.
- How come there is such a big difference/discrepency between the 2 numbers.
- All the columns in the chart have to be at zero or have to add up to 100/to be 100.
- Cross the street on/at/using/inside the crosswalk.
- What's the name of this street/What street is this?
- Do you know where the white paper is (at)?
- Turn to the middle/centerfold of the newspaper.

Thank you
who owns that car / whose car that is

add up to 100

at the crosswalk

white paper is at
Could you please help me with these sentences?

Thank you
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 Philip's reply was promoted to an answer.

An estimated 75% of the UK working population spend their working day sitting on a chair _ not sitting on the right chair can cause abdominal, spine, neck or leg damage.

Which word fits correctly ? A Consequently, B However, C Because or D Subsequently