\[ \text { Let } \begin{aligned} U & =\{1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20\}, \\ C & =\{1,3,5,7,9,11,13,15,17,19\} . \end{aligned} \] Use the roster method to write the set $C^{\prime}$. \[ c^{\prime}= \] (Use a comma to separate answers as needed. Use ascending order.)

Step 1 ：Let \(U = \{1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20\}\) and \(C = \{1,3,5,7,9,11,13,15,17,19\}\).

Step 2 ：The set \(C^\prime\) is the complement of set \(C\) in \(U\). This means that \(C^\prime\) contains all the elements in \(U\) that are not in \(C\).

Step 3 ：To find \(C^\prime\), we can subtract the elements of \(C\) from \(U\).

Step 4 ：So, \(C^\prime = \{2, 4, 6, 8, 10, 12, 14, 16, 18, 20\}\).

Step 5 ：Final Answer: \(\boxed{\{2, 4, 6, 8, 10, 12, 14, 16, 18, 20\}}\)