Green’s Dictionary of Slang

(US campus) to get a grade C.

1965		Wisconsin State Jrnl 17 Jan 1-2: Getting an ‘A’ on a test is ‘aceing’ it or ‘hooking’ it. Getting an ‘F’ or failing is called ‘flagging’.
1976		Eble Campus Sl. Nov. 3: hook – to make the grade C: I hooked the test; I got a hook on the test.