What is the Topology?

I- Topology is a mathematical study that allows us to see the relationship between knots and physics, chemistry, or molecular biology.
II- For mathematicians, a knot is a continuous, closed curve without double points, located in a three-dimensional space.
III- The study of knots is dedicated to resolving the issue of when two knots are equivalent.
IV- The complexity of knots is measured by the number of crossings in the simplest planar projection of the knot.
a) Only I and II are correct.
b) Only II and III are correct.
c) Only III and IV are correct.
d) All statements are correct.