Meaning of 'engrossed'

[intel]

Test No. incompl/inter-26 "The Ants and the Grasshopper", question 5

They were so ......... in their work that they didn't notice a grasshopper.

(a) enveloped
(b) engrossed
(c) encompassed
(d) enlarged

Test No. incompl/inter-26 "The Ants and the Grasshopper", answer 5

They were so engrossed in their work that they didn't notice a grasshopper.

Correct answer: (b) engrossed

Your answer was: incorrect
They were so encompassed in their work that they didn't notice a grasshopper.
_________________________

what does "engross" mean?

[Torsten]

They were so busy with their work that they didn't notice a grasshopper.

TOEIC listening, photographs: One of the wonders of the World