Bruce ____ (prefer) playing football to playing basketball.

Valentine's Day(情人节) is on February 14th every year. On this day, people send valentines(情人卡)to their loved ones, Valentine's Day is a special time to tell how much you care about a person.
Many people send candy in hearted shaped("心"状的)boxes to people they love. Flowers are also presents that people send on Valentine's Day. Valentine cards with words are often used by many people.
Can you guess who gets the greatest number of Valentine cards in the United States each year? Is it mother or father, sister or brother? Is it uncle or aunt? Is it the special friend? No, it isn't!
Mothers get a lot of cards, but school teachers get the most each year. Do you know who sends the most? Children do. Children send five times as many on February 14th as adults do.

如图，在棱长为a的正方体ABCD-A₁B₁C₁D₁中,P为A₁D₁的中点,Q为A₁B₁上任意一点,E,F为CD上任意两点,且EF的长为定值,则下面四个值中不为定值的是

解：∵BC=DE（已知）

∴BC+CD=DE+CD（____）

即：____=____

又∵AB∥EF（已知）

∴____=____

∴在△ABD与△FEC中

∠A=∠F（已知）

____=____（已证）

____=____（已证）

∴△ABD≌△FEC（____）

∴∠ADB=∠FEC（____）

∴AD∥CF（____）