您的要求无法解析为可安装的软件包集。 （在laravel）

Question

我正在使用此命令安装包

  

作曲家需要jenssegers / mongodb

输出就是这个

 Using version ^3.0 for jenssegers/mongodb ./composer.json has been
 created Loading composer repositories with package information
 Updating dependencies (including require-dev) Your requirements could
 not be resolved to an installable set of packages.

   Problem 1
     - jenssegers/mongodb v3.0.0 requires mongodb/mongodb ^1.0.0 -> satisfiable by mongodb/mongodb[1.0.0, 1.0.1, 1.0.2].
     - jenssegers/mongodb v3.0.1 requires mongodb/mongodb ^1.0.0 -> satisfiable by mongodb/mongodb[1.0.0, 1.0.1, 1.0.2].
     - jenssegers/mongodb v3.0.2 requires mongodb/mongodb ^1.0.0 -> satisfiable by mongodb/mongodb[1.0.0, 1.0.1, 1.0.2].
     - mongodb/mongodb 1.0.2 requires ext-mongodb ^1.1.0 -> the requested PHP extension mongodb is missing from your system.
     - mongodb/mongodb 1.0.1 requires ext-mongodb ^1.1.0 -> the requested PHP extension mongodb is missing from your system.
     - mongodb/mongodb 1.0.0 requires ext-mongodb ^1.1.0 -> the requested PHP extension mongodb is missing from your system.
     - Installation request for jenssegers/mongodb ^3.0 -> satisfiable by jenssegers/mongodb[v3.0.0, v3.0.1, v3.0.2].

   To enable extensions, verify that they are enabled in those .ini
 files:
     - /etc/php5/cli/php.ini
     - /etc/php5/cli/conf.d/05-opcache.ini
     - /etc/php5/cli/conf.d/10-pdo.ini
     - /etc/php5/cli/conf.d/20-apcu.ini
     - /etc/php5/cli/conf.d/20-json.ini
     - /etc/php5/cli/conf.d/20-mysql.ini
     - /etc/php5/cli/conf.d/20-mysqli.ini
     - /etc/php5/cli/conf.d/20-pdo_mysql.ini
     - /etc/php5/cli/conf.d/20-readline.ini   You can also run `php --ini` inside terminal to see which files are used by PHP in CLI mode.
> 
> Installation failed, deleting ./composer.json.

我的composer.json就是这个

{
    "name": "laravel/laravel",
    "description": "The Laravel Framework.",
    "keywords": ["framework", "laravel"],
    "license": "MIT",
    "type": "project",
    "require": {
        "php": ">=5.5.9",
        "laravel/framework": "5.2.*"
    },
    "require-dev": {
        "fzaninotto/faker": "~1.4",
        "mockery/mockery": "0.9.*",
        "phpunit/phpunit": "~4.0",
        "symfony/css-selector": "2.8.*|3.0.*",
        "symfony/dom-crawler": "2.8.*|3.0.*"
    },
    "autoload": {
        "classmap": [
            "database"
        ],
        "psr-4": {
            "App\\": "app/"
        }
    },
    "autoload-dev": {
        "classmap": [
            "tests/TestCase.php"
        ]
    },
    "scripts": {
        "post-root-package-install": [
            "php -r \"copy('.env.example', '.env');\""
        ],
        "post-create-project-cmd": [
            "php artisan key:generate"
        ],
        "post-install-cmd": [
            "Illuminate\\Foundation\\ComposerScripts::postInstall",
            "php artisan optimize"
        ],
        "post-update-cmd": [
            "Illuminate\\Foundation\\ComposerScripts::postUpdate",
            "php artisan optimize"
        ]
    },
    "config": {
        "preferred-install": "dist"
    } }

我尝试了不同的解决方案，还将我的php版本从5.5.9升级到5.6.2。什么是可能的解决方案？