1. scientists believe that ancient ancestors of all animals were (1 point) a) single-celled prokaryotes that reproduced asexually. b) single-celled eukaryotes that sometimes grew in colonies. c) multicellular organisms that were probably autotrophic. d) multicellular organisms with an alternation of generations lifecycle. 2. the cambrian explosion resulted in the evolution of the first (1 point) a) dinosaurs and mammals. b) representatives of most animal phyla. c) bacteria. d) land animals.

1.The correct answer is option B, single-celled eukaryotes that sometimes grew in colonies

Reason – Single celled species are originally the main ancestors of all animals because after evolution and classification, these species evolved into multicellular organisms which later on further diversified into different generas, species and classes. Living in colonies allowed these single celled species to produce sexually

2.The correct answer is option B, representatives of most animal phyla

Reason – The cambarian explosion is considered as the most evolutionary phase in the Earth’s history. All major animal body plans including Ctenophora, Poriferas, Cindaria, Chordata, Hemichordata, Echinodermata, Nematoda, Artropoda, Platyhelminthes, Mollusca, Annelida, Brachiopoda etc. occurred during this period.