21.
Consider the following statements regarding the symptoms of wilt of arhar and choose the correct answer:
1. The susceptible plants are attacked when young - about five to six weeks old
2. The first symptom is the premature yellowing of the leaves
3. The leaves appear to be affected progressively from the bottom towards the top
4. Sudden wilting is rare

22.
Auxanometers have been devised to measure

26.
Consider the following statements and choose the correct answer:
1. The carbon, nitrogen and various cycles in nature operate to conserve the limited amount of usable matter on the earth
2. The flow of energy is both cyclic and one-way
3. The transfer of energy through a biological community begins when the energy of sunlight is fixed in a green plant by photosynthesis
4. It is estimated that only 8 percent of the energy of the sun reaching the planet strikes green plants and that only 2 percent of this is utilized in photosynthesis

30.
The first visual symptoms of red-rot of sugarcane appear