Question: What is the principal difference between an array and a matrix?

1. A matrix has two dimensions, while an array can have three or more dimensions.
2. An array is a subtype of the data frame, while a matrix is a separate type entirely.
3. A matrix can have columns of different lengths, but an array's columns must all be the same length.
4. A matrix may contain numeric values only, while an array can mix different types of values.

Answer: The correct answer of the above question is Option A:A matrix has two dimensions, while an array can have three or more dimensions.