Question

in order to observe your crystals as they grow, you...
use your five senses.
use your intuition.
use your estimation skills to make general observations.
use your four senses.

Explanation:

To observe crystals growing, the most direct way is by using the five senses (sight, touch, smell, taste, hearing if applicable in a safe way). Intuition is not a reliable method for scientific - like observation. Estimation skills are for rough calculations rather than direct observation. There are five senses, not four.

Answer:

use your five senses.