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)