Why are spectral lines useful in classifying stars?

According to the earth science reference tables, during which geologic time period were the continents of north america,south america, and africa closest together?

According to a recent survey, the local government wants to classify people according to their income earning capacity. they want to do so in order to provide special facilities for the poor. who among the four individuals will be classified as poor? a. joseph earns $2.25 per day b. maria earns $1.50 per day c. rosita earns $2.00 per day d. tim earns $ 1.00 per day

Because its government strictly controls its economy, north korea has a economy. a. command b. mixed c. traditional d. free market