Character development refers to the creation of a character with their own personalities, own complexities, and opinions. Whereas, internal conflict refers to the inner struggle of the character. The internal characteristics make the character look more graphic and thoughtful.
Hence, the example which best describes the character development through internal conflict is B.Cole applies to university when he finally stops doubting his own intelligence.
In the above sentence, the character develops by overcoming his internal conflict of doubting his own intelligence. In the other sentences, the sentence a,c, and d talk about the external conflicts faced by the characters