Answer:
#Prompt the user to enter the miles.
Miles = float(input('Enter the miles to convert into kilometer: '))
#Check the miles.
if Miles >= 0 :
    #Convert the miles to kilometers.
    Miles_To_km = Miles*1.6
    #Display the result.
    print (Miles, "miles equivalent to", Miles_To_km, "kilometer.")
    #Prompt the user to enter the gallons.
    Gallon = float(input('Enter the gallons to convert into liter: '))
    #Check the validity of the Gallons entered.
    if Gallon >= 0:
        #Convert gallons into liters.
        Gal_To_Lit = Gallon*3.9
        #Display the result.
        print (Gallon, "gallons equivalent to", Gal_To_Lit, "liters.")
        #Prompt the user to enter the pounds.
        Pound = float(input('Enter the pounds to convert into kilograms: '))
        #Check the validity of the Pounds entered.
        if Pound >= 0:
            #Convert pounds into kilograms.
            Pounds_To_Kg = Pound*0.45
            #Display the result.
            print (Pound, "pounds equivalent to", Pounds_To_Kg, "kilograms.")
            #Prompt the user to enter the temperature in Fahrenheit.
            f = float(input('Enter the temperature in Fahrenheit: '))
            #Check the value to be not greater than 1000.
            if f < 1000:
                #Convert Fahrenheit into celsius.
                F_To_C = (f -32)*5/9
                #Display the result.
                print (f, "Fahrenheit equivalent to", F_To_C, "celsius.")
            #Otherwise.
            else:
                
                #Display the error message.
                print ("Invalid temperature (greater than 1000) !!!")
        else:
            #Display the error message.
            print ("Pounds cannot be negative !!!")
    else:
            #Display the error message.
            print ("Gallons cannot be negative !!!")
else:
    #Display the error message.
    print ("Miles cannot be negative !!!")
Explanation: