The most obvious & complicated feature of all living organisms is: (1) The ability to sense their surroundings or environment and respond

The most obvious & complicated feature of all living organisms is:

(1) The ability to sense their surroundings or environment and respond to these environmental stimuli.

(2) Reproduction - sexual or asexual - for production of progeny of own kind.

(3) The ability to growth in size due to cell division.

(4) Presence of complex organs systems such as digestive and nervous system.