Found 4 phrases starting with OB:

object lesson	A lesson taught using a familiar or unusual object as a focus.	Rate it:
object lesson	A punishment intended as a deterrent to others.	Rate it:
object lesson	An example that typifies a principle.	Rate it:
object lesson	Anything used an example or lesson which serves to warn others as to the outcomes that result from a particular action or behavior, as exemplified by the fates of those who followed that course.	Rate it:

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A lessons

B words

C fingernails

D erasers