Four Different Uracil Auxotrophs of Neurospora, a Eukaryotic Mold, Are $\quad\quad\quad\quad\quad\quad\quad { \text { Compound } }$

Four different uracil auxotrophs of Neurospora, a eukaryotic mold, are tested for growth on uracil and uracil precursors. The data are shown in the following table. A plus sign (+) means growth. $\quad\quad\quad\quad\quad\quad\quad { \text { Compound } }$
$\begin{array} { | l | l | l | l | l | l } \hline & \text { A } & \text { B } & \text { C } & \text { D } & \text { Uracil } \\\hline \text { Mutant 1 } & + & + & + & - & + \\\hline \text { Mutant 2 } & - & - & + & - & + \\\text { Mutant 3 } & + & - & + & - & + \\\text { Mutant 4 } & - & - & - & - & + \\\hline\end{array}$
-Neurospora can be grown as haploids or diploids. Haploid mutants 1 and 2 are fused to make a diploid. If both 1 and 2 carry recessive mutations, on which compounds will the diploid be able to grow?