I want the an swer in english

Okay, here is the solution in English:

a) A vacuum flask reduces heat loss through the following mechanisms:

• The vacuum between the double walls prevents heat transfer by conduction and convection.
• The silvered surfaces of the inner walls reflect heat radiation, thus minimizing heat loss by radiation.
• The stopper prevents heat loss by conduction and convection through the neck of the flask.

b) Nalukwago's vacuum flask might be faulty due to:

• Loss of vacuum: Air has entered the vacuum space, allowing heat to escape via conduction and convection.
• Damaged silvering: The silvered surfaces are compromised, reducing their ability to reflect heat radiation.
• A loose or damaged stopper: This allows heat to escape easily through the neck of the flask.

c) Electric cables sag during the day and become taut at night due to thermal expansion and contraction.

• Daytime: Higher temperatures cause the metal cables to expand, increasing their length. This extra length results in the cables sagging.
• Nighttime: Lower temperatures cause the metal cables to contract, decreasing their length. This contraction makes the cables taut.