长期的物种进化使两栖动物既能活跃在陆地上，又能游动于水中。利用虚基类建立一个类的多重继承，包括动物(animal，属性有体长，体重和性别)，陆生动物(ter_animal，属性增加了奔跑速度)，水生动物(aqu_animal，属性增加了游泳速度)和两栖动物(amp_animal)。其中两栖动物保留了陆生动物和水生动物的属性。 要求: animal只有带参的构造函数。其他函数根据需要自行设置

以下是利用虚基类和多重继承实现的代码，满足题目要求：

#include <iostream>
using namespace std;

class animal {
protected:
    double length;
    double weight;
    char gender;
public:
    animal(double len, double wt, char gen) {
        length = len;
        weight = wt;
        gender = gen;
    }
};

class ter_animal : virtual public animal {
protected:
    double running_speed;
public:
    ter_animal(double len, double wt, char gen, double speed) : animal(len, wt, gen) {
        running_speed = speed;
    }
};

class aqu_animal : virtual public animal {
protected:
    double swimming_speed;
public:
    aqu_animal(double len, double wt, char gen, double speed) : animal(len, wt, gen) {
        swimming_speed = speed;
    }
};

class amp_animal : public ter_animal, public aqu_animal {
public:
    amp_animal(double len, double wt, char gen, double r_speed, double s_speed) : animal(len, wt, gen), ter_animal(len, wt, gen, r_speed), aqu_animal(len, wt, gen, s_speed) {
    }
};

int main() {
    amp_animal frog(10.5, 0.2, 'M', 3.5, 2.0);
    cout << "Frog's length: " << frog.length << endl;
    cout << "Frog's weight: " << frog.weight << endl;
    cout << "Frog's gender: " << frog.gender << endl;
    cout << "Frog's running speed: " << frog.running_speed << endl;
    cout << "Frog's swimming speed: " << frog.swimming_speed << endl;
    return 0;
}

这里定义了4个类，其中`animal`为虚基类，`ter_animal`和`aqu_animal`分别继承了`animal`，同时也是虚基类。`amp_animal`继承了`ter_animal`和`aqu_animal`，并且通过虚基类继承`animal`，这样可以避免出现二义性。

在`main`函数中，我们创建了一个`amp_animal`的实例`frog`，并输出了它的各项属性。