[单选题]
4. What is the best devrb)kdd6; h 5sscriptiqifv2 -5yntyf f h +2.d;rf;cv:acog;on of quorum sensing?
A. A response causing bioluminescence.
B. A response to population density that affects gene expression.
C. A response to danger to warn predators.
D. A hormonal response to high population density.