Cells secrete acids and bases to maintain the proper pH for enzymes to work, and most human enzymes work at a optimal pH of 7.4, but other enzymes work at many different pH ranges. Given these facts, cells secrete acids and bases to maintain what among the following options: - Chemical energy  - resistance  - increases a body's strength  - To keep their body heat.  - most human enzymes  - aerobic capacity  - allow growth  - temperature
most human enzymes

The digestive system breaks food into nutrients for the body, and another nutrient to be concerned with is iron. Given these facts, what does the digestive system break food into for the body among the following options: - sugar  - fatty  - iron  - lipids  - edible  - liquid  - matter  - Energy
iron

Muscles can only contract, and muscles in the upper arm called biceps are used to flex the arm. Given these facts, what can only contract among the following options: - nerves  - Epidermis  - the skin  - strong  - biceps  - Bend  - lungs  - forces
biceps

Carbon may be stored in sedimentary rock for millions of years, and limestone is a type of sedimentary rock. Given these facts, where might carbon be stored for million of years among the following options: - In sediment  - stomach  - limestone  - refrigerator  - weathering  - loose dirt  - Earth  - body water

limestone