Question

which reason best explains why dead specimens must be used with transmission electron microscopes?
electrons pass over the specimen.
the lights that are used are harmful to the specimens.
specimens are placed in a vacuum.
the image that is produced is two dimensional.

Explanation:

1. Analyze Option 1: Transmission electron microscopes (TEM) use electrons that pass through the specimen (not over), so this is incorrect.
2. Analyze Option 2: TEM does not use light; it uses electrons, so this reasoning is wrong.
3. Analyze Option 3: TEM requires a vacuum environment. Living specimens would not survive in a vacuum (as they need air, water, etc.), so specimens must be dead to be placed in a vacuum for TEM imaging. This is a valid reason.
4. Analyze Option 4: The 2 - dimensional nature of the image from TEM is about the type of image produced, not why dead specimens are needed. So this is incorrect.

Answer:

C. Specimens are placed in a vacuum.