GRE北美题No4-2.docVIP

No. 4-1 SECTION 3 Questions 1-7 A certain code uses only the letters K, L, M, N, and O. Words in the code are written from left to right. Code words are only those words that conform to the following conditions: The minimum length for code words is two letters, not necessarily different from each other. K cannot be the first letter in a word. L must occur more than once in a word, if it occurs at all. M cannot be the last letter in a word, nor the next-to-the-last letter. N must occur in a word if K occurs in the word. O cannot be the last letter in a word unless L occurs in the word. 1. Which of the following letters could be placed after O in L O to form a code word exactly three letters long? (A) K (B) L (C) M (D) N (E) O 2. If the only kinds of letters that are available are K, L, and M, then the total number of different code words, each exactly two letters long, that it is possible to make is (A) 1 (B) 3 (C) 6 (D) 9 (E) 12 3. Which of the following is a code word? (A) K L L N (B) L O M L (C) M L L O (D) N M K O (E) O N K M 4. What is the total number of different code words exactly three identical letters long that it is possible to make? (A) 1 (B) 2 (C) 3 (D) 4 (E) 5 5. The code word M M L L O K N can be turned into another code word by carrying out any one of the following changes EXCEPT (A) replacing every L with an N (B) replacing the first M with an O (C) replacing the N with an O (D) moving the O to the immediate right of the N (E) moving the second L to the immediate left of the K 6. Which of the following is not a code word but could be turned into one by changing the order of the letters within the word? (A) K L M N O (B) L L L K N (C) M K N O N (D) N K L M L (E) O M M L L 7. Which of the following could be turned into a code word by replacing the “X” with a letter used in the code? (A) M K X N O (B) M X K M N