I-765: Prior employment authorization DATES?

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My spouse previously worked through OPT, and had previous employment authorization.

On form I-765, it asks:

11. Have you ever before applied for employment authorization from USCIS?

--> in his case, YES

Which USCIS Office?

--> easy: the _____ service center.

Date(s)

--> Not sure what to put???

Options I'm thinking that are possible:

a) date initially applied for employment authorization

b) employment authorization priority date

c) employment authorization I-797C receipt NOTICE DATE

d) employment authorization I-797C approval notice RECEIPT DATE

f) employment authorization I-797C approval notice NOTICE DATE

g) date range of approval employment

What date(s) to put here? Thank you for your help!