Why is this the answer?

The answer is key because this riddle is a very clever puzzle that describes the two biggest jobs of a key: opening a locked door and starting a car. It uses word pictures to show how something so small has such incredible power. Let us look at the first two lines of the riddle. It says, "What force and strength cannot get through. I, with a gentle touch, can do." Think about a big, heavy door that is locked. This door is very strong and is built to keep people safe inside or out. If you tried to use only your strength or a big force, like a heavy push or a hard kick, to open that locked door, you probably would not be able to get in. You would be using a lot of force, but the lock is too strong. That is where the key comes in. You do not need to be super strong to use a key. You just need to insert the key into the lock and turn it with a "gentle touch." The little cuts on the key are the secret, special shape that tells the lock to move its tiny metal parts and open up the door. A tiny, gentle turn of a key can do what all the strength in the world cannot. It is a small puzzle piece that unlocks the secret of the door. Now let us look at the second part of the riddle: "Many in the street would stand. Were I not a friend at hand." Imagine a street full of cars and houses. Keys are friends to both. For a house, the key lets the door stop "standing" locked and lets you go inside. For cars, this clue works even better. If you did not have a key to start your car, it would just "stand" there, completely stuck and unable to move. The car is standing still in the street because it needs the key, which is its "friend at hand," to turn on the engine and let you drive away. You can push a car a little, but you cannot move it far or fast without the key. The key is small, but it has the great power to make many big things stop standing still and start moving or open up, which is what makes it such a good friend.