The answer is: False. 
 If a logarithm is written without a base it IS NOT a natural logarithm.
 
The explanation is shown below:
 1. If a logarithm is written without a base, you must assume the base is 10. It is written as below:
 log(x)
 2. It is important to know that the base a natural logarithm is the irrational number e. It is written as below:
 ln(x)