Identify the alkyne in the following sequence of reactions:

Question

$$\begin {array} {1 1} (1)\;H_3C-C \equiv C- CH_3 & \quad (2)\; H_3C-C H_2-C \equiv CH \\ (3)\; H_2C = CH -C \equiv CH & \quad (4)\;HC \equiv C-CH_2 - C \equiv CH \end {array}$$