[ابو بيشو]

Explain
In unit three and practice test (2) sentence N.(3) you used "by cash". I've checked Cambridge Online Dictionary and Oxford Dictionary and Longman Online Dictionary and I didn't find that they use "by cash". Please explain that. Thanks in advance.
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Dictionaries report what is most common. But that doesn't mean that other prepositions are necessarily wrong. By cash is used, especially when followed by or credit card or when both payment systems are being discussed in the same passage. Please see the answer here.