Answer:
1.Beginner , 2.Intermediate , 3.Advanced
These are the three stages of language development
The infinitive phrase in this sentence is to speak clearly, and it is used as a subject of the sentence. What/who is essential to being understood? To speak clearly.
Umm well have a good setting and reasoning for why you want chemistry between them. And for good chemistry give them a history and challenge there chemistry with different moods and obstacles. thats just my opinion i love writing.