In an accumulator $($one address$)$ based processor, assume the instruction size is $32-$bit. The most significant $6$ bits are used for the opcode, the next $6$ bits are used for the function field, which tells the processor the exact operation of the instruction, and remaining $20$ bits are used to encode the memory address. What is the maximum possible number of instructions this machine can support?

O A$.4096$

$$ B$.64$

O C$.$ None

O D$.32$