I received a PM asking me to comment. This stuff can get complicated, so I'll mostly try to use examples and show what they mean, rather than use "formal" grammar language.
Has been and have been are both used with the present perfect tenses, which is used when we want to talk about something that started in the past but (1) is still going on right now in the present OR (2) is still relevant / true today.
Eg:
I have been to France. (Sometime in the past, I went to France, and that fact is still true today.)
She has been living in this house for awhile. (She started living in this house sometime in the past and she still lives in this house now. She may keep living in this house in the future.)
The first is an example of plain present perfect - there's no other verb besides the "have been" construction.
The second is an example of present perfect continuous or present perfect progressive - an "ing" verb after "been," indicating an ongoing action.
The have vs. has decision is based on the subject: I have, you have, s/he/it has, we have, they have. On the GMAT, in general, your choice will usually be between s/he/it has and they have, so we generally think of "has" as singular and "have" as plural.
"had been" basically follows similar parameters, but for the past perfect instead of present perfect. In this case, "had" doesn't change depending on the subject (whether it is singular or plural) - it's just always "had."
On this test, we use the past perfect to indicate something that happened in the past before something else that also happened in the past OR something that happened in the past and was still going when another, later past even then occurred. You can indicate these two events either directly (by, for example, referencing a date in the past) or indirectly (by, for example, using simple past tense to indicate the action that occurred later in time).
(There are some other uses for past perfect, but they generally don't come up on this test.)
In 1990, John had been the top student at his school for several years. (First, John had been the top student prior to 1990 and still was the top student in 1990. After that... we don't know.)
The teacher thought that John had been a particularly outstanding student. (First, at some unspecified time, John was an outstanding student; then, at some unspecified but LATER time, the teacher had this thought about John.)
Now here's past progressive:
Before the teacher entered the room, John had been cheating on the exam. (First, John was in the act of cheating on the exam. Later, the teacher walked in. Did John stop because the teacher walked in? Or had he already stopped for some other reason before she walked in? We don't know - but the OG prefers to interpret this as: John cheated. Then John stopped. Then the teacher walked into the room.)
present perfect progressive:
John has been cheating on the exam ever since the teacher left the room. (John started teaching sometime in the past, when the teacher left the room. He's still cheating right now. He may continue cheating for some indeterminate amount of time into the future.)
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