Englishfor English speakers
effective
Adjective
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An effective strategy, treatment, method, etc is one that works well as planned.
Teachers are using instructional strategies that are most effective in helping students learn.
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If you have effective command, consent, control, etc., you have it in practice but not officially.
The students had effective control over what the teacher would include on the test.
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If a law, agreement, change, etc. becomes effective, it officially begins.
The new rules about ball size are effective next season.
effective
Preposition
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You use effective to say when something starts officially.
Effective next week, all employees will wear the new uniform.
density
Noun
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Density is how much stuff fits in a particular area.
The population density of Singapore is one of the highest in the world.
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The density of a material is how closely packed its atoms are.
The density of water is higher than the density of steam.