Answer:
No
Explanation:
External validity refers to being able to apply the results of the research experiment to real life situations. Therefore based on the information provided in the question it can be said that Dr. Rajah's experiment does not have external validity. This is mainly due to the fact that brain teasers are problems that does not reflect on real world problems or events.
History is defined as a time of historical, written documents, so they would have some very limited amount of inscriptions, sometimes one line long, that they can use.
They would use those and complement this information with archaeological information from the time.
The Yellow River and the Yangtze River
Because Germany tried to set up an alliance with Mexico saying that if they helped they would let them have part of the land