When it comes to regular verbs, the way to create past tense is to add -ed (if the verb ends with a consonant), or -d (if the verb ends with a vowel).
So, the verb smile ends in e, which means that you only need to add -d to create past tense. The correct answer is:
Mona Lisa smiled mysteriously.
The noun clause is "who made the initial discovery"? this is the direct object (answer d!) of the sentence: it's the object of the verb "know": you know what? you know who made the initial discovery
Fables are normally short stories conveying a moral. I would say B