Which of the following measure could not improve the settling efficiency in sedimentation tank？ （ ）。 A: To increase the surface area of the tank B: To increase the flow rate C: To improve the performance of flocculation before sedimentation D: To recycle the sludge to improve the size of particles

Bacterial ribosomes contain about 65% rRNA and 35% protein; they have a diameter of about 18 nm and are composed of two unequal subunits of ___________ and a combined sedimentation coefficient of 70S. A: 20S and 50S B: 30S and 40S C: 30S and 50S D: 30S and 60S