consonant /t/ contrasts with consonant /d/

[playagain]

Please help me about my reporting in my English Class...
I was asked to report about consonant /t/ contrasts with consonant /d/ (consonant contrast /d/ and /t/)...
My problem is that I have no idea about this topic..
Please do help me... I need to report this in front of the class next week.. Please give me some ideas or some links(websites) for me to study... :) :) :)

Thanks in advance...
Any help will be much appreciated :) :) :)
-playagain

[Hi_there_Carl]

Maybe this will help: Flap consonant - Wikipedia, the free encyclopedia

[playagain]

but how flap consonants related to my topic? where is the contrast of /t/ with consonant /d/???