What does throughout their shifts mean?

[Germannn]

English Language Tests, Intermediate level

ESL/EFL Test #881 "Taxi Terms", question 4

Taxi drivers ......... up passengers throughout their shifts.

(a) lift
(b) pick
(c) carry
(d) snatch

English Language Tests, Intermediate level

ESL/EFL Test #881 "Taxi Terms", answer 4

Taxi drivers pick up passengers throughout their shifts.

Correct answer: (b) pick
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I wonder what "shifts" means here.
thanks a lot.

[Beeesneees]

A shift is their period of work: one of two or more recurring periods in which different groups of workers do the same jobs in relay.

Taxi drivers might work the day shift, the evening shift or the night shift.
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Cheers m' dears!