1. The following propositions are correct ( ) in number.
(1) Very small real numbers can form a set;
(2) The set $\left\{y \mid y=x^{2}-1\right\}$ and $\left\{(x, y) \mid y=x^{2}-1\right\}$ are the same set;
(3) $1 、 \frac{3}{2} 、 \frac{6}{4} 、\left|-\frac{1}{2}\right|, 0.5$ These numbers form a set with five elements;
(4) The set $\{(x, y) \mid x y \leqslant 0, x 、 y \in \mathbf{R}\}$ refers to the set of points in the second and fourth quadrants.
(A) 0
(B) 1
(C) 2
(D) 3
- 1. A.
(1) The reason it is wrong is that the elements are uncertain;
(2) The former is a set of numbers, the latter is a set of points, the types are different;
(3) There are repeated elements, it should be three elements;
(4) This set also includes the coordinate axes.