Explain why Meg, rather than Cal or Mr. Murry, had to be the one who rescued Charles Wallace.

Meg
certainly seems like an unlikely choice as the one to return to Camazotz to rescue Charles
Wallace. However, as we learn in chapter 12, Mr. Murry and Calvin can't do it. First of all, Mr.
Murry, although he is the most experienced with tessering, is told flat-out by Mrs. Whatsit that
he cannot be allowed to go. They all know that his attempt would end in failure. Calvin is
similarly told he cannot go when he volunteers. It is...