(a) When zero is divided by any number, the quotient is zero. (b) The product of any number and zero is still zero. (c) The reciprocal of zero is zero. (d) The sum of two opposite numbers is zero.

12.1.61×104 has precision and significant digits of () respectively.

(a) Accurate to 1%, with three significant figures; (b) Be accurate to 1% and have three significant figures.

(c) To the nearest one percent, with five significant figures.

13. Among the six numbers -(-2), (-1)3, -22, (-2)2, -∣-2∣, (-1)2n (n is a positive integer), the number of negative numbers is.

1 (B) 2 (C) 3 (D) 4。

14. The time difference between Paris and Beijing is -7 hours (a positive number means that the same moment is several hours earlier than Beijing time). If Beijing time is July 2nd 14:00, then Paris time is ().

(a) July 2nd 21(b) July 2nd 7: 00 (c) July 2nd 7: 001(d) July 2nd 5: 00.

15. If a represents 1 cube, b represents the superposition of two cubes, and c represents the superposition of three cubes, then the geometry of the superposition of seven cubes in the picture on the right is ().

(A) (B) (C) (D)

16. As shown in the figure, it is known that the straight line a∨b is () under the following conditions.