Complete the following by suppling intermediates
`MeCH_(2) C=- CH overset(Na//liq. NH_(3))(to) [A] overset(EtBr)(to)[B]`

Explanation

`MeCH_(2)C-= CH overset("N/A in liq. NH"_(3))(to) MeCH_(2) C-= C^(-) N/A^(+) overset(EtBr)underset(-N/ABr)(to) underset("Hex -3- yne (B)")(MeCH_(2)C-= CEt)`