fixed tense

Author: hmayes

paper/basic_training.pdf

@@ -158,7 +158,7 @@ \section{Scope of this document}
 \section{Science topics}
 \label{sec:science}
 A new practitioner does not have to be an expert in all of the fields that provide the foundation for our simulation methods and analysis of the data produced by these methods. 
-However, grasping some key concepts from each of these disciplines, described below, are essential for every practitioner of molecular simulations. This section serves as a preface for Section~\ref{sec:basics} and suggestions for further reading on these subjects are provided throughout the document.
+However, grasping some key concepts from each of these disciplines, described below, is essential for every practitioner of molecular simulations. This section serves as a preface for Section~\ref{sec:basics} and suggestions for further reading on these subjects are provided throughout the document.
 In each subsection, we begin by highlighting some of the critical topics from the corresponding area, then describe what these are and why they are important to molecular simulations.
 
 \subsection{Classical mechanics}