Question

Fill in the blank with the future perfect continuous tense of the word given in the bracket:
By 2p.m. the girl ____________ at the bus stand for hours. (wait)
a) Was waiting
b) Will have been waiting
c) Has been waiting
d) None of these

Answer 1

Hint: Read the question very carefully, twice. It is highly suggestive of the correct answer. The future perfect continuous tense is used when something will continue up until a particular event or time in the future.

Complete answer:
The future perfect continuous, also sometimes called the future perfect progressive, is a verb tense that describes actions that will continue up until a point in the future. The future perfect continuous consists of will + have + been + the verb's present participle (verb root + -ing).

Reading the above analysis and the grammatical rule of tenses, we will proceed with the process of elimination of alternatives that don't have the rule applied.
The first option doesn't have 'been', moreover it has the past participle of the verb, making it the incorrect alternative.

Option B is the correct answer because it has all the aspects of the rule covered. Will+have+been+wait (root form of the verb)+ing is the future perfect continuous tense.

'Has been waiting' is the present continuous tense and therefore is the incorrect answer as the question very clearly asks for the answer to be in the future perfect continuous tense.

Now that we have found the correct alternative, the last option stands totally irrelevant.

Note:
Tenses have a very predefined set of rules, once you learn them, there is a negligible chance of getting your answers incorrect. Also, never read the question hurriedly, a lot of students make this mistake.