How to pronounce ' t ', ' k ' , ' p ' behind " s "

I find the following pronunciation that my English teacher teached were a bit different with the pronunciation that native English speaker sounded.

discuss for 'c' behind 's' , my teacher sound 'k' as for 'key', but I feel that most of native English speakers sound 'g' as for 'go', the same questions for the words-excuse, discover, and so on.

mistake for 't' behind 's', it should sound 't' as for 'tea' ? OR it should sound 'd' as for 'day' ? , the same question for words ' western ', 'Mister' and so on.

transport – for 'p' behind 's', it should sound 'p' as for 'pen'? OR it should sound 'b' as for 'bed', the same question for words 'express', 'passport' , 'sport' and so on.

Please can you let me which pronunciation are correct ?  Thank you.

Pronounce them the way you are taught. There are many different ways people talk, or slang in english. It really depends on how you personally talk. Of course there is the right way, but if it is easier for you to say it a certain way, then go with that. Not everyone talks the same. You mentioned the "T's" and the "D's". They are gonna sound the same. It doesnt really matter. As long as you spell the words right.
Don't Fret.  After a while, you wont even notice it.

Thank you very much for kind help. I can understand what you said. But please can you tell me which pronumciation is the right ways. I want to speak it in a right way.

The first answer that you received is a pretty good answer, actually. You're going to have to make a decision about the English accent you choose to use. Pronunciation varies among native speakers. At our English school, we select foreign teachers from western Canada only, so that there is a uniform accent spoken in the school. That doesn't mean it's the 'right' one, but more that our students won't get confused with a mixture of accents. My advice is to try to speak with the accent that your teacher uses. And if you really don't like your teacher's accent, then find a teacher who speaks in a way that is pleasing to you, and go with that.

Yeah, "And if you really don't like your teacher's accent, then find a teacher who speaks in a way that is pleasing to you, and go with that."
I'd like accent of American south, but it seems weird if an asian got an accent like American south people.
Any suggestion?

try to pronouce letters as they are

 you get the occasional different word

but you just need to learn which they are.

for 't' behind 's', it should sound 't' as for 'tea' ? OR it should sound 'd' as for 'day' ? , the same question for words ' western ', 'Mister' and so on.

transport – for 'p' behind 's', it should sound 'p' as for 'pen'? OR it should sound 'b' as for 'bed', the same question for words 'express', 'passport' , 'sport' and so on.

t as in tea= is becoz T sounds like Tea & Tee, like B= Bee , Behind,its the spelling killing you, not the pronouncation i feel.

transport,pen, same

b is bed,bad,bulk,boobies,balls,bong

express,passport,sport,pilgrim,pain in ass,punish, all same.

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