我从GitHub克隆了一个项目，并尝试使用Composer安装软件包，我安装后没有遇到任何问题。我运行composer安装。不幸的是，我犯了这些错误，我无法理解，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.
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