Which excerpt from "The Enigma Machine” supports the claim that German soldiers accidentally helped the Allies figure out the Enigma codes?

With the right settings, the recipient only needed to type in the encrypted text and the message would light up in plain text.
To use the Enigma machine, an operator typed a message into the machine, which would be scrambled by three rotors . . .
The Polish intelligence developed the "bomba", a complicated system of wires and rotors to scan and decode messages within hours.
Typing in messages was a boring task, so operators took shortcuts, like choosing three letters in a row or other simple, predictable patterns.

Question

Which excerpt from "The Enigma Machine” supports the claim that German soldiers accidentally helped the Allies figure out the Enigma codes?

With the right settings, the recipient only needed to type in the encrypted text and the message would light up in plain text.
To use the Enigma machine, an operator typed a message into the machine, which would be scrambled by three rotors . . .
The Polish intelligence developed the "bomba", a complicated system of wires and rotors to scan and decode messages within hours.
Typing in messages was a boring task, so operators took shortcuts, like choosing three letters in a row or other simple, predictable patterns.