2. Let a, b and c are variables. Which of the following is a postfix expression?
(A) a/(b + c)；
(B) xabc/+；
(C) abc + /；
(D) /a + bc.

18. Determine the speed of rotation of a synchronous generator with parameters 480V/50Hz/six poles/delta-connection.(A) 600rpm(B) 1000rpm(C) 1200rpm(D) 2000rpm

19. A four-pole, 60Hz induction motor supplies 15kW to a load at 5% slip. Choose a false statement.(A) Synchronous speed is 1800 rpm(B) Rotor speed is 1710 rpm(C) Rotor frequency is 3Hz(D) Load torque is 41.7N·m

20. A single-phase transformer is rated at 220/440V, 10kVA. Leakage reactance measured from the low-voltage side is 0.24Ω. Choose a false statement.(A) Base impedance at the low-voltage side is 4.84Ω(B) Base impedance at the high-voltage side is 19.36Ω(C) Leakage reactance at the low-voltage side is 0.050 pu(D) Leakage reactance at the high-voltage side is 0.012 pu

1. Suppose we have a byte-addressable machine, i.e., each byte is accessed via an address. Let the locations for an array be allocated in a row-major manner, and each element of an array takes 4 bytes. Assume that the address of the first byte of the array is 500 in all the following cases. Which of the following is true?(A) The address of the element A10 in an array declared as A100 is 24586；(B) The address of the element A1030] in an array declared as A[100[300] is 177899；(C) The address of the element A[10] in an array declared as A[100] is 536；(D) The address of the element A1030 in an array declared as A100300 is 76457217.

3. Let a = 3, b = 8, c = 6 and d = 5. What is the value of the prefix expression × ba + dc?(A) 13；(B) 14；(C) 15；(D) 16.

4. The ADT stack can be defined by the following axioms:(aStack.createStack()).isEmpty() = true(aStack.push(item)).isEmpty() = false(aStack.createStack()).pop() = error(aStack.createStack()).getTop() = error(aStack.push(item)).getTop() = item(aStack.push(item)).pop() = aStackFor the following expression:(((((((aStack.createStack()).push(1)).push(2)).pop()).push(3)).pop()).pop()).isEmpty()what is the value returned?(A) an item；(B) a stack；(C) true；(D) false.

5. Suppose a stack is implemented by a variable top and an array B[4]. Note that top denotes the index of the last element pushed. Initially, the stack is empty. Then the following operations are performed in order:push(1), push(2), pop(), push(3), push(4), pop(), getTop(), push(5), pop(), push(6).Which of the following is true in the end?(A) B[0] = 3；(B) B contains 4 integers available；(C) An overflow occurred, so the operations could not be completely done；(D) top is 2.

6. Let the height of a tree be the number of nodes along the longest path from the root node to the leaf nodes. Consider the integers 30, 41, 25, 29, 94, 37, 70, 23, 65, 75, 68, 67 in order to create a binary search tree. Which of the following is true?(A) The node for 37 is a leaf node；(B) The root node is 41；(C) The node for 70 has only one child；(D) The height of the tree is 5.

7. Consider a complete binary tree with exactly 5000 nodes, implemented with an array starting from index 0. Suppose that a node has its value stored at index 999 in the array. What index is the value stored at for this node's left child?(A) 999；(B) 1999；(C) 998；(D)2998.

8. Consider a tree with A as the root node. The left and right child of A are B and C, respectively. The left and right child of B are D and E, respectively. The left and right child of E are F and G. What is the order of the nodes processed in the pre-order traversal?(A) A-B-E-D-F-G-C；(B) D-B-F-E-A-G-C；(C) A-B-D-G-F-E-C；(D) A-B-D-E-F-G-C.