It is best to avoid serving cow's milk until the infant reaches the age of ________.
1 answer:
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If we guide ourselves with the Moh´s scale:
Material scratches apatite → material is harder than 5.
Material is scratched by corundum → material is softer than 9.
Conclusion:
The hardness of the unknown material stands between 5 and 9.
Note:
Both apatite and corundum are defining materials (reference materials in the Moh´s scale). So, you can also give an answer using defining materials:
"It can either be an orthoclase feldspar, a quartz or a topaz".
Hope it helped,
BiologiaMagister
<u><em>This answer is dedicated to JaySL</em></u>
