Restoring 2011 macbook air back to factory settings - which option?

hi all,

newbie england here.

great forums these, found loads of info out, except question.

looking @ restoring purchased macbook air factory settings. have rebooted using cmd + r , gone disk utility. intention erase hard drive, have noticed there 2 options, 1 erase hard drive , 1 erase ssd, can tell 1 supposed erase please.

 

you have erase partition (i guess call "hard drive") called "macintosh hd" (unless renamed it), mac os x resides on.
indented volume below actual ssd.

 

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