Why is the symbol x avoided in algebra?

The X looks too similar to the multiplication sign. So, to avoid multiplication signs that look like x's, people use *, ( ), · , instead of an X. This avoids much confusion.

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands