At the time of speaking
1(a) Please be quiet ,I am concentrating on doing my Math.
(b) It is so noisy.Our neighbours are quarreling.
in the middle of doing something,but not necessarily at the time of speaking
2(a) I am learning English in the moment, I want to get high score in my TOEFl .
(b) I am reading a Dan Brown book--Digital Fortress.
around the time of speaking
3(a) I am helping my mother to wash the dishes today.
(b) I am enjoying the holiday this week. I hope you will have a pretty good once too.
4(a) The price of goods in the market is getting high.
(b) My English is getting better.
5(a) I am living in my friend's apartment until my house is ready.
(b) I am using the radio to listen to music until I have my Ipod.