Question 20 – 24
Use the information in the passage to match the advantages and disadvantages of the two systems: horizontal flow system and down-flow system (listed A—H) below.
Write the appropriate letters A-H in boxes 20-24 on your answer sheet.
The advantage of the downflow system is 20……………….; however, 21………………and 22…………………The two advantages of the horizontal system are 23………………..and 24………………….In comparison with the downflow system, the horizontal system is less effective.
A. it requires several beds
B. it is easier to construct
C. it builds on a gradient
D. it doesn’t need much attention
E. it produces less sludges
F. it isn’t always working
G. it needs deeper bed
H. it can deal with more heavily polluted water
20.