According to Charles Darwin’s observations:

The correct answer is Option (4) → All of the above.

Charles Darwin made a long sea voyage round the world in the ship H.M.S. Beagle. His observations on this voyage led him to the theory of evolution by natural selection. Each of the first three options states one of his conclusions.

Option (1) Present-day organisms have similarities to those that lived millions of years ago. — Correct statement, but it is only one of the correct points, so on its own it is not the answer. Darwin concluded that living forms share similarities, to varying degrees, among themselves and also with life forms that existed millions of years ago.

Option (2) Species evolve over time through gradual changes. — Correct statement, but it is only one of the correct points, so on its own it is not the answer. He saw that new forms of life arose at different periods while others became extinct, so there has been a gradual evolution of life forms.

Option (3) Populations possess inherent variations that help them adapt and survive in their natural environments. — Correct statement, but it is only one of the correct points, so on its own it is not the answer. He noted that every population has built-in variation. Individuals whose characteristics help them survive better in natural conditions leave more offspring than others, which is the basis of natural selection.

NCERT Extract:
Evolution of Life Forms – A Theory – “… Based on observations made during a sea voyage in a sail ship called H.M.S. Beagle round the world, Charles Darwin concluded that existing living forms share similarities to varying degrees not only among themselves but also with life forms that existed millions of years ago. Many such life forms do not exist any more. There had been extinctions of different life forms in the years gone by just as new forms of life arose at different periods of history of earth. There has been gradual evolution of life forms. Any population has built in variation in characteristics. Those characteristics which enable some to survive better in natural conditions (climate, food, physical factors, etc.) would outbreed others that are less-endowed to survive under such natural conditions.”