The following passages may contain a comma splice or a fused sentence. Select the answer that eliminates the problem in the original. The field of developmental psychology deals with changes in mental and behavioral performance over time, the field began with a focus on
child psychology, it has grown to track changes throughout a lifetime.
The field of developmental psychology deals with changes in mental and behavioral performance over time. The field began with a focus
on child psychology, it has grown to track changes throughout a lifetime.
The field of developmental psychology deals with changes in mental and behavioral performance over time. Although the field began
with a focus on child psychology, it has grown to track changes throughout a lifetime.

The field of developmental psychology deals with changes in mental and behavioral performance over time. Although the field began  with a focus on child psychology, it has grown to track changes throughout a lifetime.

Explanation:

The original passage is-

The field of developmental psychology deals with changes in mental and behavioral performance over time, the field began with a focus on child psychology, it has grown to track changes throughout a lifetime.

Now, the problem in the above passage is in the use of the comma between the three independent sentences. To make the passage complete and correct, the first part of the passage will be taken as a single sentence. Then, with the remaining two sentences, the conjunction "although" can be used to present and join the two independent sentences.

Thus, the correct sentence is the second option.