Plz answer my previous 2 Questions​

The table shows dates and appearance of index fossils. which rock layers can be dated most precisely? a) a layer containing both a fossil 4 and a fossil 3 b) a layer containing both a fossil 2 and a fossil 3 c) a layer containing both a fossil 1 and a fossil 4 d) a layer containing both a fossil 1 and a fossil 2

Which type of respiration takes place when there is no oxygen present

Which is an important function of normal flora? a. aid with bone marrow production. b. crowd out pathogenic bacteria. c. destroy digestive track pathogens. d. manufacture iron in the bloodstream.