In the given question a sentence is given with a blank and you have to choose an appropriate word from the given options that can fill the sentence making that grammatically and meaningfully complete. The influence of early childhood experiences on brain development is not only __________ but also long-lasting, shaping aspects such as learning, health, behavior, and future productivity. 

The sentence describes the importance of early childhood experiences on brain development. Given the context, the blank needs to be filled with a word that conveys importance or strong impact. Significant is the correct choice because it means important or considerable, which fits the context of the sentence, emphasizing the lasting influence of childhood experiences. Trivial means insignificant or unimportant, which contradicts the intended meaning of the sentence. Negligible also means very small or insignificant, which would weaken the impact described in the sentence. Transient means temporary or short-lived, which doesn't match the idea of a long-lasting influence as mentioned in the sentence.