Mendel gave the theory of inheritance after researching the process using the pea plants. He used pea plants for his research for multiple reasons, one of which was they were relatively easy to grow and have various easily visible characteristics. The characteristics observed by Mendel included plant height, flower color, flower position, pool color, pool shape, seed color, and seed shape. All these seven characteristics can be easily observed in the pea plant making the research easier.
hence, the answer is option B - they can all be easily observed'.