A- Gravity. I believe it is gravity since that is the only one that makes sense in this situation. I hope i helped! :)
Contraction is the answer
There are so many examples for that in different areas, like biology experiment carried out in our lab recently.
Here's one linhttps://www.creative-biogene.com/support/Lentiviral-Vectors-the-Application-for-CAR-T-Therapies
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