In order to find a name of a Hydrocarbon molecule, we need to look for the main carbon chain first, this will be the chain with the highest number of carbon atoms, and in this molecule, we have 4 carbon atoms, therefore we have a 4 carbon molecule, the prefix for this type of molecule is But.
We also have a triple bond in the first carbon, the suffix for triple bonds is "yne"
Therefore, if we add all these informations, we will have 1-butyne, letter A