What made the black plague especially terrifying

Why was russia drawn into a conflict with germany after ausria-hungary declared war on serbia ?

Who did the first work in creating vaccines

Using only this chart, which step would you take first to compare the standard of living in these countries? add the gdp numbers for the countries to get a total. divide each gdp number by its country's population. subtract each population number from its country's gdp. multiply the population number by the gdp for each country.