C-02-Q166mediumsingle_mcq
If a Secchi disk cannot be seen at a depth of 25-30 cm, it indicates —
If a Secchi disk cannot be seen at a depth of 25-30 cm, it indicates —
- aLow natural food
- bNatural food is available
- cOxygen deficiency
- dHigh alkalinity
If a Secchi disk cannot be seen at a depth of 25-30 cm, it indicates —