1) Do you say "a packet or a box of washing powder"?
2) Is it possible to use the word "washing-up liquid"?
3) They don't smoke or cut down on cigarettes because they know they harm our health (??) They are harmful
I'll give you American English terms. I'm not sure of British English terms for these things.
1. ... a box of detergent.
2. ... dish-washing soap
or
... dish-washing liquid
3. The antecedents for the different uses of "they" need to be clarified.
http://grammar.ccc.commnet.edu/grammar/pronouns.htm
People don't smoke or cut down on cigarettes because they know that cigarettes harm their health. Cigarettes are harmful.
Sure, I can help answer your questions.
1) To determine whether to say "a packet or a box of washing powder," you can consider the common usage of the terms in your region or specific context. In general, both "packet" and "box" can be used to refer to the packaging of washing powder. However, the specific term most commonly used will depend on the local language conventions or personal preference.
2) Yes, it is possible to use the term "washing-up liquid." "Washing-up liquid" is commonly used in British English to refer to a detergent specifically used for washing dishes or utensils. In other variations of English, such as American English, the term "dish soap" or "dishwashing liquid" is often used.
3) The statement seems to have a missing word or phrase, but based on the information provided, it seems like the intended meaning is "They do not smoke or reduce their consumption of cigarettes because they know that cigarettes are harmful to our health." This sentence implies that the individuals are aware of the negative health effects of smoking and choose not to smoke or try to decrease their cigarette intake.