Match the parasites with their infective stages in humans:
| Parasites | Infective stage |
|---|---|
| A) Entamoeba histolytica | I) Tetranucleate cyst |
| B) Plasmodium vivax | II) Sporozoite |
| C) Ascaris lumbricoides | III) 2nd stage Rhabditiform larva |
| D) Wuchereria bancrofti | IV) 3rd stage Microfilaria |
A - I, B - IV, C - III, D - II
Find the variance of the following frequency distribution:
| Class Interval | ||||
| 0--4 | 4--8 | 8--12 | 12--16 | |
| Frequency | 1 | 2 | 2 | 1 |