concentrated nutrients and a steep salt gradient abundant shelter and concentrated nutrients a steep salt gradient and shallow water shallow water and abundant shelter
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Estuaries are called "the nurseries of the sea" because many species lay eggs and develop their young in estuaries. Which two features of estuaries support this role most?
Possibilities:
- concentrated nutrients and a steep salt gradient
- abundant shelter and concentrated nutrients
- a steep salt gradient and shallow water
- shallow water and abundant shelter

abundant shelter and concentrated nutrients