it has been thousands of years 为什么用的是has而不是have 用中文解释

在这个句子中，主语 "it" 指的是一个单数名词，因此需要使用单数形式的动词。虽然 "thousands of years" 表示的是复数，但它实际上是作为一个量词来修饰主语 "it" 的，而不是作为主语来使用。因此，正确的表达是 "it has been thousands of years"（已经过去了几千年了）。

相关问题

10086的千位是什么，用Python计算

10086的千位是1。

在 Python 中，可以使用整数除法运算符（`//`）和取模运算符（`%`）来计算一个数的千位。例如：

num = 10086
thousands_place = num // 1000  # 除以 1000 得到千位
print(thousands_place)  # 输出: 10

上面的代码会输出 10，即 10086 的千位是 1。

注意：在 Python 中，整数除法会自动向下取整。因此，如果要计算小数位，需要使用浮点数除法运算符（`/`）。例如，计算 10086 的百位就可以这样写：

num = 10086
hundreds_place = (num % 1000) / 100  # 取模 1000 得到个位、十位、百位，再除以 100 得到百位
print(hundreds_place)  # 输出: 8.06

上面的代码会输出 8.06，即 10086 的百位是 8。

Define a Pet class that stores the pet’s name, age, and weight. Add appropriate constructors, accessor, and mutator functions. Also define a function named getLifespan that returns a string with the value “unknown lifespan.” Next, define a Dog class that is derived from Pet. The Dog class should have a private member variable named breed that stores the breed of the dog. Add mutator and accessor functions for the breed variable and appropriate constructors. Redefine the getLifespan function to return "Approximately 7 years" if the dog’s weight is over 100 pounds and "Approximately 13 years" if the dog’s weight is under 100 pounds. Next, define a Rock class that is derived from Pet. Redefine the getLifespan function to return “Thousands of years”. Finally, write a test program that creates instances of pet rocks and pet dogs that exercise the inherited and redefined functions.

Sure, here is a possible implementation of the classes and a test program in Python:

class Pet:
    def __init__(self, name, age, weight):
        self._name = name
        self._age = age
        self._weight = weight
    
    def getName(self):
        return self._name
    
    def getAge(self):
        return self._age
    
    def getWeight(self):
        return self._weight
    
    def setName(self, name):
        self._name = name
    
    def setAge(self, age):
        self._age = age
    
    def setWeight(self, weight):
        self._weight = weight
    
    def getLifespan(self):
        return "unknown lifespan"
    

class Dog(Pet):
    def __init__(self, name, age, weight, breed):
        super().__init__(name, age, weight)
        self._breed = breed
    
    def getBreed(self):
        return self._breed
    
    def setBreed(self, breed):
        self._breed = breed
    
    def getLifespan(self):
        if self.getWeight() > 100:
            return "Approximately 7 years"
        else:
            return "Approximately 13 years"
    

class Rock(Pet):
    def getLifespan(self):
        return "Thousands of years"
    

# Test program
rock1 = Rock("Rocky", 1000000, 0.1)
rock2 = Rock("Stony", 2000000, 0.2)
dog1 = Dog("Buddy", 5, 50, "Golden Retriever")
dog2 = Dog("Spike", 3, 150, "Mastiff")

print(rock1.getName(), rock1.getLifespan())  # Rocky Thousands of years
print(rock2.getName(), rock2.getLifespan())  # Stony Thousands of years
print(dog1.getName(), dog1.getLifespan())    # Buddy Approximately 13 years
print(dog2.getName(), dog2.getLifespan())    # Spike Approximately 7 years

dog1.setWeight(80)
print(dog1.getName(), dog1.getLifespan())    # Buddy Approximately 13 years

In this implementation, `Pet` is the base class that stores the common attributes of pets, such as name, age, and weight. It provides accessor and mutator functions for these attributes, as well as a default implementation of `getLifespan` that returns "unknown lifespan".

`Dog` is a derived class that adds a private attribute `breed` and corresponding accessor and mutator functions. It also redefines the `getLifespan` function to return different values based on the weight of the dog.

`Rock` is another derived class that specializes `Pet` for pet rocks. It simply redefines the `getLifespan` function to always return "Thousands of years".

The test program creates instances of `Rock` and `Dog`, and calls the inherited and redefined functions on them to verify that they work as expected. It also demonstrates how to use mutator functions to update the weight of a dog and recompute its lifespan accordingly.