A PDF must be put into an external program after being exported to be edited, you can't make direct changes to it. This eliminates answer choice A.
You can print documents with other extensions besides .pdf, such as those of Word documents and such, it doesn't have to be a .pdf. This eliminates answer choice B.
Since you can't directly edit a PDF, C is a possible answer.
Files don't have to be saved as a .pdf, especially just for the first time. Whenever you save a file, first time or not, you can save it as anything, and there's no reason to have to save it as a .pdf. This eliminates answer choice D.
So the answer is C. it contains material you don't want changed.
Hope this helps!
Answer:
Implicit type casting means the type casting done by the compiler during compilation of program whereas Explicit type casting means the programmer explicitly type casts the variables. This is the difference implicit and explicit type casting.
Explanation:
Type casting means the conversion of one data type into another data type. There are two types of type casting. They are Implicit type casting and Explicit type casting.
<u>Implicit type casting:</u> The type casting which is done by the compiler during the compilation of a program. This occurs when we assigning smaller data type to larger data type and also both the data type are compatible. Below example clears the above concepts.
Ex:

In the above example " i " is " int " data type whereas " l " is long data type but as we assigned the value of " i " to " l ". Here " int " and " long " are compatible data types and we assigned smaller data type ( int - i ) to larger data type ( long - l ) implicit type casting occurs.
<u>Explicit type casting:</u> The type casting which is done by the programmer explicitly to convert one data type into other data type. If we want to assign a value of larger data type to smaller data type explicit type casting is required. Below example clears the above concepts.
Ex: 

In the above example " d " is " double " data type whereas " l " is " long " data type. Here we are explicitly type casting to change larger data value ( double - d ) to smaller data value ( long - l ).
A string variables??? I'm not sure does this have any multiple choice
It known as the smart systems
It make decision by describing and analyzing the available data in a predictive or adaptive manner thereby performing an efficient and smart actions based on that analysis
A lot of smart systems evolved from micro systems