Thanks for the question! So for these kinds of questions that ask for something that was true of something in the passage, you’re often going to be able to find it directly in the passage (stated, of course, in some sneaky way), or it is going to be a very direct inference you can make (like if the passage says “Bob ate an apple” and one of the answer choices is “Bob has eaten fruit before”).
For this specific question, we’re going to have to direct our attention to the sentence starting at line 30, and the key part is between lines 33 and 34. Here, we’re told that certain products remained unidentified because of “the dangers of working with highly radioactive materials,” and what does this tell us? Well, it tells us that the physics community in the 1930s was aware of the dangers of working with radioactive substances, and that’s what (E) tells us. It would typically be helpful to think about where the passage talks about members of the physics community and their work, though that occurs basically throughout the whole passage here, so really go through it with a fine-toothed comb.
Hope this helps! Feel free to ask any other questions that you might have.
