Why do we need to use "to start with"

[June]

Business English Courses, Elementary Level

ESL/EFL Test #71 "Chit Chat: At the garage", question 6

Mechanic: To start ......... It's losing a lot of oil.

(a) at
(b) for
(c) in
(d) with

Business English Courses, Elementary Level

ESL/EFL Test #71 "Chit Chat: At the garage", answer 6

Mechanic: To start with It's losing a lot of oil.

Correct answer: (d) with
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Why do we need to use "with"

June

[Conchita]

'To start with' is the idiom normally used to mean 'for a start' or, more informally, 'for starters'. Other similar phrases are: first of all, first off, first or firstly.