To solve this problem, we need to identify the first stable product of $$CO$_2$ fixation in sorghum. Sorghum is a C$_4$ plant, and the process of $$CO$_2$ fixation in C$_4$ plants is different from that in C$_3$ plants.$\newline \bullet$In C$_4$ plants, the initial fixation of $$CO$_2$ occurs in the mesophyll cells.$\newline \bullet$The enzyme phosphoenolpyruvate carboxylase (PEP carboxylase) catalyzes the reaction between phosphoenolpyruvate (PEP) and $$CO$_2$ to form oxaloacetic acid (OAA).$\newline \bullet$Oxaloacetic acid is the first stable product of $$CO$_2$ fixation in C$_4$ plants like sorghum.$\newline$Therefore, the correct answer is Option 2: Oxaloacetic acid.