What is 160km/h in metres per second?

$$1 \text{ km} = 1000 \text{ m}$$ $$160 \text{ km} = 160 \times 1000 \text{ m} = 160000 \text{ m}$$

$$\frac{160000}{3600} \text{ m/s} = \frac{1600}{36} \text{ m/s} = \frac{400}{9} \text{ m/s} \approx 44.44 \text{ m/s}$$

The closest option is A.

The final answer is $\boxed{\text{A. } 44.44 \text{m/s}}$.

19. What is the implication of the hazard symbol below?

The hazard symbol shown, an exclamation mark within a diamond, is a GHS (Globally Harmonized System) pictogram. It generally indicates less severe health hazards.

Among the given options:

• A. Health hazard (This is a broad category, but the symbol does indicate a health hazard).
• B. Highly inflammable (This is indicated by a flame symbol).
• C. Irritant (This is one of the primary implications of the exclamation mark symbol, specifically for skin and eye irritation).
• D. Toxic (This is usually indicated by a skull and crossbones symbol for acute toxicity or the health hazard symbol for specific target organ toxicity).

The most specific and common implication for this symbol among the choices is Irritant.

The final answer is $\boxed{\text{C. Irritant}}$.

20. The instrument used for measuring the diameter of a thin copper wire is -----

To measure the diameter of a thin copper wire, an instrument capable of high precision is required.

• A. Vernier calipers are used for measuring external and internal dimensions and depths, typically with a precision of 0.02 mm or 0.05 mm.
• B. A micrometre screw gauge is specifically designed for measuring very small lengths or diameters, such as that of a thin wire, with a higher precision, typically 0.01 mm.
• C. A Laser lever is not a standard instrument for measuring diameter.
• D. An Inclinometer measures angles of slope or tilt.

Therefore, the micrometre screw gauge is the most suitable instrument for this task.

The final answer is $\boxed{\text{B. Micrometre screw gauge}}$.