Answer:
Difficulty
Explanation:
Space exploration was the last thing the world could have thought of dabbing into because the idea of moving away from the earth and flying in the sky wasn't even an easy one for man, hence the difficulty attached with going into other planets was a big success.
Many trials were made before the eventual success experienced, this many difficulties man overcame is what is meant by barrier in this sense.
<span>B. A struggle or problem that causes the events in a story to progress
The conflict is always a problem that causes the story to continue and unravel.
Hope this helps ;)</span>
Two things. Wave in water or wave with a hand.
