1. Math is my favorite subject. (Here, "Math" is the subject of the sentence and functions as the noun).
2. History can be a fascinating subject. (Again, "History" is the subject and acts as a noun).
3. The environment is a crucial subject for our future. (The entire phrase "The environment" functions as the noun subject).
4. Learning new languages is a rewarding subject. (This time, the subject is a gerund phrase, acting as a noun).
5. The study of human behavior is a complex subject. (Another example of a phrase functioning as the noun subject).