<p>On the PSAT Practice Test in PR's 11 Tests book (it's the last test) on #14 on the writing can anyone help me? Here's the problem, I put $ $ around all the parts that were underlined.</p>
<p>A number of scientists $have begun$ to speculate $whether$ life $actually began$ as crystals of clay rather $than$ as organic molecules. $No error$</p>
<p>I put $have begun$ since number is singular, isn't it? But the book says there's no error. Help, anyone?</p>