A theory which repeatedly fails to confirm the expected predictions after extensive research: probably needs to be modified probably is incorrect requires more research time should be maintained indefinitely

Answer: -

Is probably incorrect.

Explanation: -

According to the theory of scientific method, the second step after observation is formulation of hypothesis to explain the observed phenomena.

If the predictions of a long-standing theory are found to be in disagreement with new experimental results, the theory may be discarded as a correct description of the phenomena.

Thus a theory which repeatedly fails to confirm the expected predictions after extensive research Is probably incorrect.