Fill in the blank with the correct tense of the verb given.
I am sleepy. I _________ (work) all night.

- According to the context of the given sentence, the speaker feels sleepy because he was working all night.
- Present perfect continuous tense is used to express an action that started in the past and is still going on or has a connection with the present.
- It follows the structure: sub + has/have + been + V1 + ing + obj + for/since + time.
- Example: I have been painting the walls since morning.
- In the given sentence, although the speaker's work has finished, he stresses the fact that he feels sleepy because he worked all night.
- So, 'have been working' is the correct filler for the given blank.
- Complete sentence: I am sleepy. I have been working all night.