A dichotomous key is a series of choices between alternative characteristics that is used to identify organisms. Check all features of a dichotomous key.

a. Oak Tree

Explanation:

A producer can be define as an autotrophic organism which is capable of producing food in the form of simple inorganic molecules such as carbohydrates by the process of photosynthesis (using light energy from the sun) or through chemosythesis (using chemical energy). Producers belong to the first trophic level in the food chain and other organisms are dependent on them for their food and energy requirements.

Among the given examples, Oak tree is the correct one, because of the fact that oak tree is a shrub of genus Quercus. It belong to the group of autotrophs therefore, it is capable of producing it's own food by the process of photosynthesis.