Present Perfect Continuous

 PRESENT PERFECT CONTINUOUS

Use:

- Actions that began in the past and continue up to the present moment.
"My back hurt! I've been digging in the garden."

- Emphasis on the duration of the action.
"How long have you been reading this book?"

- Actions expressing anger, irritation or criticism.
"I am freezing! I have been waiting for hours!"

Form:

have/ has + been + gerund (-ing form)

Expressions of time:

For, since, how long



TIME TO EXERCISE!

http://www.englishgrammarsecrets.com/presentperfectsimpleorcontinuous/menu.php 
(read the explanation and in the end of the page you have links for 5 exercises)

http://www.ego4u.com/en/cram-up/grammar/prepersim-preperpro

http://english-zone.com/verbs/prsperfcont.html