Final answer:
The characteristic of the Kidd system antibodies is that they are usually strong and stable during storage.
Step-by-step explanation:
The characteristic of the Kidd system antibodies is that the antibodies are usually strong and stable during storage. This means that the antibodies can be stored for extended periods without losing their effectiveness.
They are not usually IgM antibodies, which are typically associated with primary immune responses. Additionally, the Kidd system antibodies are not typically implicated in delayed hemolytic transfusion reactions.