The correct answer is: A. Exposed.
To discover something is to find it or learn about it for the first time. To expose something is to make it known or visible. To reveal something is to make it known or visible by removing something that is covering or concealing it. To conceal something is to hide it or keep it from being seen. To contend is to argue or fight against something.
In the context of the question, the word “discovered” is most closely related to the word “exposed.” This is because to discover something is to find it or learn about it for the first time, which is similar to exposing something, which is to make it known or visible. The other options are not as closely related to the word “discovered.” For example, to reveal something is to make it known or visible by removing something that is covering or concealing it, which is not the same as finding something or learning about it for the first time. To conceal something is to hide it or keep it from being seen, which is also not the same as finding something or learning about it for the first time. To contend is to argue or fight against something, which is not related to finding something or learning about it for the first time.