Which two forces act directly on objects that are unable to be viewed by the unaided eye?
electromagnetic and strong
gravitational and electromagnetic
strong and weak
weak and gravitational

strong and weak

Explanation:

There are four fundamental forces in the universe:

- Gravitational force: this force acts between all objects having mass, and it is always attractive. Its strength is very weak compared to the other forces, so its effects can only be seen on very massive objects (such as planets, stars, etc.)

- Electromagnetic force: this force acts between all objects having electrical charge, and it can be either attractive or repulsive. The effects of this force can be osbserved both on daily-life objects or on small particles.

- Strong nuclear force: this force is responsible for keeping neutrons and protons together in the nuclei of the atoms, and it acts on very small scales. Due to its very short range of action, the effects of this force can only be observed on microscopic scales.

- Weak nuclear force: this force is responsible for the decays of atoms (for example, it is responsible for certain radioactive decays). Due to its very short range of action, the effects of this force can only be observed on microscopic scales.

Based on the definitions of the four forces listed above, we can state that the two forces that act on objects unable to be viewed by unaided eye are

strong and weak

Because effects of the the other two forces (gravitational and electromagnetic) can be also observed on large-size objects.