Science and technology is the primary productive force because () A. Science and technology is the standard of social progress B. China should implement the strategy of rejuvenating the country through science and education C. Science and technology have a profound impact on all factors of productivity and play a key role in economic growth

Productivity = science and technology × (labor force + labor tool + labor object + production management)
The above formula shows that science and technology are not only the direct productive forces in reality, but also have a special position in the elements of productive forces. The multiplication effect of science and technology strongly expresses its primary position and role in productive forces
So choose C

Standard precipitation symbol
Put Na2CO3 and NaHCO3 into a beaker filled with distilled water. After a while, NaHCO3 precipitates out, and ask why it should be marked with ↓.
I don't think the following two people understand the essence of the problem. What I want to know is why it should be marked. This is the key point.
What I want to know is that this problem is the same as the principle of adding Cao into saturated Ca (OH) 2?
You can discuss the bonus points (the first one is the one who answers
13-3-10-14:30 before the end of the supplement decisive points.

First of all, NaHCO3 precipitates crystals because of saturation. It is already a solid and not in solution, so the sign of precipitation should be added
Na2CO3 + CO2 + H2O ------ 2nahco3 results in the supersaturation of NaHCO3 in solution
This problem is similar to the principle of adding Cao in saturated Ca (OH) 2

That = =, = = =? Can't be typed out, or is there this symbol!
That should be = there are other things on it, such as heating and catalyst, which are not mentioned on the Internet

When there is no gas in the reactant to take part in the reaction and there is gas in the product, it is necessary to add ↑ after the gas

Is ignition in the chemical equation the same as the symbol of heating (triangle)?

The meaning of ignition and heating is different
In chemistry, ignition has no sign. Ignition means to ignite the reactant with open fire or high temperature
In chemistry, the symbol of heating is a triangle, which is placed on the top of the equal sign in the chemical reaction formula. Heating means to use high-temperature objects to conduct indirect heat conduction to the reactants, so as to raise the temperature of the reactants

Is the product of two square roots of a number negative

If it is positive or negative, the product must be negative; if it is 0, the product is 0;

What's the difference between a negative number and a signed number?

Well, negative numbers are less than signed numbers
Any number (except 0) has a sign, such as + 3 (positive three), but we often omit the positive sign
However, the negative sign before the negative number cannot be omitted
So negative numbers are less than signed numbers, and signed numbers also include positive numbers
If you agree with my answer, please click the "select as satisfied" button below,

Add the operation symbol and bracket to the number to make the result 24
8 3 4 3＝24
8 4 3 3＝24
15 9 1 5＝24
7 6 5 13＝24

8X3X（4－3）

8 = 2 with proper operation symbol bracket between numbers

8÷8+8÷8=2

4 = 5 add appropriate operation symbols and brackets to the number

（4×4＋4）÷4＝5

Without changing the value of the following formula, the symbols before the brackets will become the opposite symbols:
(the third power of X + the square of 3x) - (the square of 3x y-7xy) + (the third power of 2y-the square of 3Y)

(the third power of X + the square of 3x) - (the square of 3x y-7xy) + (the third power of 2y-the square of 3Y)
=-(- X's cubic power - 3x's Square) + (- 3x's Square y + 7xy) - (- 2Y's cubic power + 3Y's Square)

That = =, = = =? Can't be typed out, or is there this symbol! That should be = there are other things on it, such as heating and catalyst, which are not mentioned on the Internet