What does this mean? being a scot believed that the art of writing lay in thrift?

[Scotty]

English Language Tests, Intermediate level

ESL/EFL Test #515 "English Slang Idioms (257)", question 1

"I know that you are good at Law, as am I, and I was wondering if you would want to ......... forces and study for the final exam together," Tim said to Paul.

(a) join
(b) jacket
(c) jaunt
(d) jam

English Language Tests, Intermediate level

ESL/EFL Test #515 "English Slang Idioms (257)", answer 1

"I know that you are good at Law, as am I, and I was wondering if you would want to join forces and study for the final exam together," Tim said to Paul.

Correct answer: (a) join
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what does this mean? being a scot believed that the art of writing lay in thrift

[Mister Micawber]

Scotsmen are unfairly but traditionally considered very thrifty at all times and for all concerns.
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Native English teacher at Mister Micawber's