(define (cddr s) (cdr (cdr s)))

(define (cadr s) 'YOUR-CODE-HERE)

(define (caddr s) 'YOUR-CODE-HERE)

(define (interleave lst1 lst2) 'YOUR-CODE-HERE)

(define (my-filter pred lst) 'YOUR-CODE-HERE)

(define (concatenate s) 'YOUR-CODE-HERE)