Explanation:

The correct answer is option 'A': The complement of the Context-Sensitive Language (CSL) is also a Context-Sensitive Language (CSL).

To understand this, let's first define the concepts involved:

1. Context-Sensitive Language (CSL):
A Context-Sensitive Language is a language that can be generated by a context-sensitive grammar. In a context-sensitive grammar, the production rules are of the form α → β, where α and β are strings of terminals and non-terminals, and the length of α is less than or equal to the length of β. These grammars are more powerful than regular grammars (Regular Languages), context-free grammars (Context-Free Languages), and regular expressions (Regular Languages).

2. Complement of a Language:
The complement of a language L, denoted by L', is the set of all strings that are not in L. In other words, if a string is in L, it is not in L', and vice versa.

Now, let's analyze the options one by one:

a) Complement of CSL is CSL:
This statement is true. The complement of a Context-Sensitive Language (CSL) is also a Context-Sensitive Language (CSL). This is because the class of Context-Sensitive Languages is closed under complementation.

b) Complement of CFL is CFL:
This statement is false. The complement of a Context-Free Language (CFL) is not necessarily a Context-Free Language (CFL). The class of Context-Free Languages is not closed under complementation.

c) Complement of RE is RE:
This statement is false. The complement of a Regular Language (RE) is not necessarily a Regular Language (RE). The class of Regular Languages is not closed under complementation.

d) Complement of non-CFL can't be CFL:
This statement is true. The complement of a non-Context-Free Language (non-CFL) cannot be a Context-Free Language (CFL). The class of Context-Free Languages is not closed under complementation.

Conclusion:
The correct answer to the question is option 'A'. The complement of a Context-Sensitive Language (CSL) is also a Context-Sensitive Language (CSL), and this is because the class of Context-Sensitive Languages is closed under complementation.