B.

Azopirillum

Azopirillum is a nitrogen-fixing bacterium in paddy fields. It is very useful soil and root bacterium. It is an associative symbiotic N₂ -fixing bacteria. When it is added to the soil, it multiplies in millions and can supply 20-40 kg of nitrogen per hectare per season. It also produces growth promoting substance like Indole Acetic acid (IAA). Gibberellins and promotes root proliferation. These substances improve the plant growth and yield.

D.

Glomus

Trichoderma is a genus of fungi that is present in all soils, where they are the most prevalent culturable fungi. Many species in the genus can be characterised as opportunistic avirulent plant symbionts. Several strains of Trichoderma have been developed as biocontrol agents against the fungal disease of plants. The various mechanisms include antibiosis, parasitism inducing host-plant resistance and competition. Most biocontrol agents are from the species. T.harzianum, T. varied and T. hamatum. The biocontrol agent generally grows in its natural habitat on the root surface and so affects root disease in particular but can also be effective against the foliar disease.

D.

gives a measure of Salmonella in the water

Biochemical Oxygen Demand (BOD) is the amount of oxygen used for biochemical oxidation by micro-organisms in a unit volume of water. Polluted water has high BOD. Thus, when sewage gets mixed with river water, BOD will increase.

B.

preformed antibodies

In passive immunity, the antibodies are produced in some other organism (eg, horse) in response to the given antigen,.These antibodies are then injected into the human body at the time of need. This is known as inoculation, eg, persons infected by tetanus, rabies, Salmonella and snake venom are given the sufficient amount of antibodies, so that they can survive.

D.

Nuclear Polyhedrosis virus (NPV)

The bacterium Xanthomonas campestris is the causative agent of plant disease, black rot of cabbage.
Bacillus thuringiensis, T. harzianum and NPV are biopesticides.