Completed test 60 test_single_quotes_sometimes_interpret_escape_characters
Completed test 61 test_double_quoted_strings_interpolate_variables
Completed test 62 test_single_quoted_strings_do_not_interpolate
Completed test 63 test_any_ruby_expression_may_be_interpolated
Completed test 64 test_you_can_get_a_substring_from_a_string
Completed test 65 test_you_can_get_a_single_character_from_a_string
Completed test 66 test_in_ruby_1_9_single_characters_are_represented_by_strings
Completed test 67 test_strings_can_be_split
Completed test 68 test_strings_can_be_split_with_different_patterns
Completed test 69: test_strings_can_be_joined

Given an array, use .join(" ") and the words in the array will be joined with a space in between them. Simply change the contents of the parenthesis to change what separates the array members.