The author seems to be mainly concerned with most fisheries' ______.

A．people should look for a baseline that can't work for a longer time
B．fisheries should keep the yield below 50% of the biomass
C．the ocean biomass should restore its original level
D．people should adjust the fishing baseline to changing situation

A．fishing technology has improved rapidly
B．the catch- sizes are actually smaller than recorded
C．the marine biomass has suffered a greater loss
D．the data collected so far are out of date