无法安装php软件包？

我从GitHub克隆了一个项目，并尝试使用Composer安装软件包，我安装该软件包时没有遇到任何问题。 我运行composer安装。 不幸的是，我有这些错误，我不能弄清楚，我该怎么办

    Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for tijsverkoyen/css-to-inline-styles 2.2.2 -> satisfiable by tijsverkoyen/css-to-inline-styles[2.2.2].
    - tijsverkoyen/css-to-inline-styles 2.2.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.
  Problem 2
    - Installation request for phar-io/manifest 1.0.3 -> satisfiable by phar-io/manifest[1.0.3].
    - phar-io/manifest 1.0.3 requires ext-dom * -> the requested PHP extension dom is missing from your system.
  Problem 3
    - Installation request for phpunit/php-code-coverage 7.0.10 -> satisfiable by phpunit/php-code-coverage[7.0.10].
    - phpunit/php-code-coverage 7.0.10 requires ext-dom * -> the requested PHP extension dom is missing from your system.
  Problem 4
    - Installation request for phpunit/phpunit 8.5.4 -> satisfiable by phpunit/phpunit[8.5.4].
    - phpunit/phpunit 8.5.4 requires ext-dom * -> the requested PHP extension dom is missing from your system.
  Problem 5
    - Installation request for theseer/tokenizer 1.1.3 -> satisfiable by theseer/tokenizer[1.1.3].
    - theseer/tokenizer 1.1.3 requires ext-dom * -> the requested PHP extension dom is missing from your system.
  Problem 6
    - tijsverkoyen/css-to-inline-styles 2.2.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.
    - laravel/framework v7.10.2 requires tijsverkoyen/css-to-inline-styles ^2.2.2 -> satisfiable by tijsverkoyen/css-to-inline-styles[2.2.2].
    - Installation request for laravel/framework v7.10.2 -> satisfiable by laravel/framework[v7.10.2].

  To enable extensions, verify that they are enabled in your .ini files:
    - /etc/php/7.2/cli/php.ini
    - /etc/php/7.2/cli/conf.d/10-opcache.ini
    - /etc/php/7.2/cli/conf.d/10-pdo.ini
    - /etc/php/7.2/cli/conf.d/20-calendar.ini
    - /etc/php/7.2/cli/conf.d/20-ctype.ini
    - /etc/php/7.2/cli/conf.d/20-exif.ini
    - /etc/php/7.2/cli/conf.d/20-fileinfo.ini
    - /etc/php/7.2/cli/conf.d/20-ftp.ini
    - /etc/php/7.2/cli/conf.d/20-gettext.ini
    - /etc/php/7.2/cli/conf.d/20-iconv.ini
    - /etc/php/7.2/cli/conf.d/20-json.ini
    - /etc/php/7.2/cli/conf.d/20-mbstring.ini
    - /etc/php/7.2/cli/conf.d/20-phar.ini
    - /etc/php/7.2/cli/conf.d/20-posix.ini
    - /etc/php/7.2/cli/conf.d/20-readline.ini
    - /etc/php/7.2/cli/conf.d/20-shmop.ini
    - /etc/php/7.2/cli/conf.d/20-sockets.ini
    - /etc/php/7.2/cli/conf.d/20-sysvmsg.ini
    - /etc/php/7.2/cli/conf.d/20-sysvsem.ini
    - /etc/php/7.2/cli/conf.d/20-sysvshm.ini
    - /etc/php/7.2/cli/conf.d/20-tokenizer.ini
  You can also run `php --ini` inside terminal to see which files are used by PHP in CLI mode.

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在Ubuntu上安装时出现问题。我添加了这个php扩展，它成功了

sudo apt-get install php-xml