What happens during the krebs cycle?

Kerb cycle is the pathway through which most of the cellular  energy (required for various metabolic  processes with in a cell)  is produced in the form of energy molecule ATP, NADH and FADH2

Explanation:

In a kerb cycle following happens sequentially -

a)Oxaloacetate (4 carbon compound) receives acetyl group (2 carbon) from acetyl CoA to produce citrate.  

b)Enzyme aconitase act on citrate to convert it into isocitrate who ich is further converted to alpha-ketogluterate thereby releasing one molecule of NADH and CO2  

c)alpha-ketogluterate is further converted into succynl-CoA accompanied by release of one molecule of NADH and CO2

d)ATP id produced while succynl-CoA is converted to succinate which is further converted to fumerate along with reduction of FAD to FADH2

e)Fumerate is then converted to malate and eventually to oxaloacetate by release of NADH

In one Kerb cycle, the end products produced are  

2 × CO2  

1 × ATP

3 × NADH

3 H+

1 × FADH2

prism b but im not for sure

the answer to your question is:

c. complementary base-pairing