Small scale industries are typically characterized by their limited capital investment, labor-intensive operations, and often operate with minimum input of materials. They do not usually rely on advan

13.
Small scale industries are typically characterized by their limited capital investment, labor-intensive operations, and often operate with minimum input of materials. They do not usually rely on advanced technology and are not exclusively located in rural areas.
The correct option is $\boxed{\text{D. operates with minimum input of materials}}$.

14.
When a p-n junction diode is forward-biased:
I. The positive terminal of the cell is connected to the p-type material, and the negative terminal to the n-type material. This is correct.
II. The depletion region (junction) becomes narrower, reducing the potential barrier. This is correct.
III. Electric current flows easily across the junction due to the reduced barrier. This is correct.
All three statements are correct.
The correct option is $\boxed{\text{D. I, II and III}}$.

15.
Global warming is primarily caused by the increase of greenhouse gases in the atmosphere.
A. Deforestation reduces the number of trees that absorb carbon dioxide, thus contributing to global warming.
B. Breeding of cattle leads to the production of methane, a potent greenhouse gas, contributing to global warming.
C. Afforestation (planting trees) helps to absorb carbon dioxide from the atmosphere, thereby reducing global warming. This is the exception.
D. Cooking of food, especially using fossil fuels or biomass, releases greenhouse gases.
The correct option is $\boxed{\text{C. afforestation}}$.

16.
In physics, the product of an object's mass and its velocity is defined as its momentum.

$$\text{Momentum} = \text{mass} \times \text{velocity}$$

The correct option is $\boxed{\text{C. momentum}}$.

17.
In the context of crop production, "supplying" refers to providing the necessary inputs for the crops to grow.
A. Application of fertilizer to crops means supplying nutrients. This fits the definition.
B. Re-planting of ungerminated stands is gap filling.
C. Watering the crop during the dry season is irrigation.
D. Distributing bagged maize to wholesalers is a post-harvest activity (marketing).
The correct option is $\boxed{\text{A. application of fertilizer to crops}}$.

18.
An alloy is a mixture of metals or a metal and another element.
A. Steel is an alloy primarily of iron and carbon. It does not contain copper.
B. Bronze is an alloy of copper, usually with tin.
C. Duralumin is an alloy of aluminum, copper, magnesium, and manganese.
D. Brass is an alloy of copper and zinc.
Therefore, steel is the alloy that does not contain copper.
The correct option is $\boxed{\text{A. steel}}$.

19.
The conversion of ammonium compounds into nitrites is the first step in nitrification, a process carried out by specific nitrifying bacteria.

• Nitrosomonas bacteria are responsible for oxidizing ammonium ($\text{NH}_4^+$) to nitrite ($\text{NO}_2^-$).
• Nitrobacter bacteria then oxidize nitrite ($\text{NO}_2^-$) to nitrate ($\text{NO}_3^-$).
• Azotobacter and Rhizobium are involved in nitrogen fixation. The correct option is $\boxed{\text{B. Nitrosomonas}}$.

20.