The correct statements to complete the given code are:$```$javagen $=$ input.next$().$charAt$(0)$;$```$Explanation:The $`$Scanner$`$ class in Java provides several methods to read input from the user, such as $`$nextInt$()`,`$nextDouble$()`,`$nextLine$()`,$ etc. However, to read a single character, we need to use the $`$next$().$charAt$(0)`$ method.The $`$next$()`$ method reads the next token $($a sequence of non$-$whitespace characters$)$ from the input, and the $`$charAt$(0)`$ method extracts the first character from the token. This assigns the input character to the $`$gen$`$ variable, which can then be used in the $`$switch$`$ statement to check the gender.The other options:$-$ Option a: $`$a $=$ input.nextInt$()$;$`$ and then $`$gen $=($char$)$a;$`$ is incorrect because it first reads an integer and then casts it to a character, which may not be the desired input.$-$ Option b: $`$a $=$ input.nextInt$()$;$`$ and then $`$gen $=$ a;$`$ is incorrect because it assigns an integer value to the $`$char$`$ variable $`$gen$`.-$ Option c: $`$a $=$ input.nextChar$()$;$`$ is not a valid method in the $`$Scanner$`$ class. There is no $`$nextChar$()`$ method.$-$ Option d: $`$gen $=$ input.nextByte$()$;$`$ is incorrect because it reads a byte value, not a character.