Trilobites are index fossils because they a. changed slowly through time c. exhibit specific characteristics b. lived over large areas of the world d. all of the above

d. all of the above

Explanation:

Trilobites are an extinct class of marine arthropods, having been one of the most frequent fossil groups in the period between the Cambric and the Devonian, and are at this time still quite biologically diverse. Trilobite fossils are considered index fossils because they change slowly over time, exhibit specific characteristics and have lived in large areas of the world.

Index fossils refer to an organism that has had a wide geographical distribution in the past, although it has lived for short periods of time, and whose remains have not only been conserved in abundance but are also easy to identify.

answer: angiosperms

dicots

angiosperms are highly evolved plants, they produce seeds which are enclosed within in a carple. these are the largest group of plants on earth. they include trees, shrubs, herbs and small flowering plants. angiosperms exhibit a flowering stage in their life cycle. the flower serves the function of reproduction and fruit formation in majority of angiosperms. dicot is the term used to describe flowering plants that have two seed leaves. dicots are plants which develop seeds which split into two parts called cotyledons. each cotyledon contains one embryo.

here, a small purple flower development indicates that the plant belongs to angiosperms and having two embryonic leaves indicates it belongs to dicots.  

it provides an alternative energy pathway for the reaction to proceed.

a catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction.

catalysts increase the rate of reaction without being used up. they do this by lowering the activation energy needed. with a catalyst, more collisions result in a reaction, so the rate of reaction increases. different reactions need different catalysts.

a catalyst works by providing an alternative reaction pathway to the reaction product. the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.