These speeches raise all kinds of issues, but at <span style="color:#0000ff;">their heart</span> are two opposing ideas <span style="color:#000000;">about what</span> <span style="color:#000000;">it takes to succeed.</span><br/><br/><b>Source</b>: <span class='_lnk_exp' title='This link has since expired, or the site is not allowing us to check the link'>https://www.newscientist.com/article/mg22129590-600-the-science-of-success-blood-or-sweat-and-tears/</span><br/><br/>Hi,<br/>One native English speaker said that it should be "<b>heart<span style="color:#ff0000;">s</span></b>" not "<b>heart</b>".<br/><br/>Do you agree with her?<br/><br/>Thank you.