Here are two of the four letter words utilizing those 4 letters in a combination that immediately come to mind.
1. grin
2. ring
I believe the answer is the first choice, which is motion.
Seeing dinosaurs is diffuclt. First of all , they are extinct also meaning that they perished. Although you can still see their remains Second, dinosaurs are trouble. They are carnivorous. Third, you can't have conversations with them, considering the animal language is the hardest. In conclusion, seeing dinosours is diffuclt because they are extinct, they are trouble, and you cant have a conversation with them.
The word explicit means something that is stated clearly and in detail. The statement leaves you unable to be confused or in doubt.
Some synonyms for this word could be: Direct, plain, obvious, straightforward, clear-cut, clearly expressed, blunt
I hope this helps :)