C. certainly
In "certainly," the "u" is pronounced like the "u" in "but."
In the other options ("community," "collection," and "education"), the "u" is pronounced like the "oo" in "boot."
B. encourage
In "encourage," the "ou" is pronounced like the "oo" in "boot."
In the other options ("recycle," "coupon," and "competition"), the "ou" is pronounced differently (ei, oo as in "soup," and ih respectively).
C. graceful
In "graceful," the "ce" is pronounced like "sh."
In the other options ("green," "manager," and "telegram"), the "ce" is pronounced differently (ee, ih, and eh respectively).
B. against
In "against," the "g" is pronounced like the "g" in "go."
In the other options ("game," "gymnast," and "great"), the "g" is not pronounced at all.
C. Christmas
In "Christmas," the "st" is pronounced like "st" in "stop."
In the other options ("school," "chemistry," and "champion"), the "st" is pronounced differently (sk, k, and sh respectively).