LeveneChargaffWatson and CrickNirenberg and Matthaei
Cells because most living things like plant life and humans are made up of cells and animals are made up of cells too!
Environmental scientists are using GPS ( It is effective but expensive) aerial monitoring (Quick but not the easiest), RFID tags, (mostly for long-term monitoring) and hidden cameras are used to study polar bear behavior without interruption to their environment.
Answer:
Nucleotide, Gene, DNA, Chromosome, Cell.
Explanation: