Which of the following is the smallest level of organization in living things? A. organ system
B. cell
C. tissue
D. organ

B. Cell

Explanation:

Order from smallest to most complex:

Cell - Tissue - Organ - Organ system.

Cells are the smallest. Multiple cells working together forms a tissue. Multiple tissues working together forms and organ. Multiple organs form an organ system.

Factors that contribute to warming include

 1. Carbon dioxide (CO2) from fossils fuel combustion.
2. Parts of earth's surface which have low reflectivity ( low albedo).
 3. Tropospheric Ozone (O3).
 4. Black carbon aerosols and soot particles.
 5. methane (CH4) from decomposition and feedlots.
6. Nitrogen oxides (N2O) from denitrification and fossil fuel combustion.

Factors that contribute to cooling include;
 1. Condenses water vapor (Cloud albedo).
 2. Parts of earth's surface with high reflectivity (high albedo).