Abiologist began studying a population of bullfrogs. in 1998, she found that
most of the male frogs croaked, but some did not. a bat species known to
prey on male frogs migrated to the area in 2005. the biologist returned to the area in 2008 and repeated population counts of male frogs. the table shows her data.

what factor most likely caused the noncroaking male population to increase
after 2004?

a) selective pressure in the form of a new predator

b) adaption of the croakers in the presence of a new predator

c) extinction of the croakers because of the new predator

d) learning to avoid the new predator