With Explorer Academy, National Geographic launches an action sci-fi series taking readers to the world’s natural wonders. The Nebula Secret (Explorer Academy #1) by Trudi Truett.  National Geographic Partners, 2018, 205 pages Reading Level: Middle Grades, ages 10-12 Recommended for: ages 10-14 Cruz Coronado has been accepted into the elite Explorers Academy, a high-tech, cutting-edge facility in Washington D. C.  He’s hoping it’s not because his Aunt Marisol is an instructor there, but soon he has other worries.  In short, it appears someone is trying to stop him: to disable, delay, perhaps even kill him.  His mother was involved in a top-secret project before she died in a work related…