Answer: D) they allow more than once hash key to map to the same index
Step-by-step explanation:
Typical hash function contain infinite domain like bit sequence with fixed length and have some finite range. It also implement byte string of some arbitrary length.
In many cases, hash function are design with permutation mapping between the range and identical size domain. Permutation are also known as one to one mapping. Mixing property are one of the desired property of hash function.
Therefore, it allow more than one hash key to map the same index.