问为什么'Col‘不工作在React引导？

EN

import React from "react";
import Container from "react-bootstrap/Container";
import Row from "react-bootstrap/Row";
import Col from "react-bootstrap/Col";

function Header() {
  return (
    <Container>
      <Row>
        <Col xs={4} md={4} lg={4} sm={4}>
          First
        </Col>
        <Col xs={4} md={4} lg={4} sm={4}>
          Second
        </Col>
        <Col xs={4} md={4} lg={4} sm={4}>
          Third
        </Col>
      </Row>
    </Container>
  );
}

export default Header;