To build neural network models for classification$/$regression tasks.

Task $1$: classify email to be spam or not, the minimum number of neurons needed in the output layer is A;

Task $2$: classify MNIST digits dataset, the number of neurons needed in the output layer is B$.$

Task $3$: predict house price, the number of neurons needed in the output layer is C$.$

What is the appropriate value for A$,$ B and C$?$