has been vs have been
- both used in present perfect continuous tense (to show an action that started in the past and is still happening at the time of speaking)
has been - use when the subject is singular
for example: She has been painting the room since I woke up in the morning.
have been - use when the subject is plural
for example: They have been running the oval for an hour.
You can get more information and tips on verb tenses at http://www.slideshare.net/stephlowe91/ielts-training-verb-tenses.