The question isn't complete and you might want to ask this in the math section.
But just to help you out, 3x means 3 times whatever "x" is.
Probably C. because it make more sense then any other answer.
Answer:
They had acquired resistance to many diseases
Without the ability to read ancient Chinese and Maya text, we would be limited to archeological findings and guesses made based on them. The fact, that we can read ancient texts, let us know for example:
the names and times of rule of many rulers,
the religious practices
some events from the past
some cultural and technological inventions such as their knowledge of astronomy
the social composition of the society
Our knowledge of urban live comes from the description of customs and occational information about who lived where and how much was paid for what services
