Sometimes dehydration causes a woman to bleed. That is actually the most common reason, however, if it is re-occuring, see a physician.
Generally, no. Girls usually develop earlier than boys.
Im not sure exactly what you mean, but if you mean what age do people usually start gynastics then you can start as young as 3, but most gymnasts that get really good start at six. The ones who start earlier burn out very quickly.
regular hours is usually when a store opens and closes
Black Friday usually begins the day after Thanksgiving. Your nearest mall would open at 5am. A lot of stores like to be competitive and will try to open earlier than others. Some will open exactly at 12 pm or sometimes earlier. Which isn't fair considering it's supposed to be on friday morning not thursday night.
A letter is postmarked on the day that it is accepted by the postal office. It will usually be the same day, but it won't be postmarked for earlier days.
a square.
Only when it has 3 or more equal sides then it is a regular polygon
Regular, although the term is more usually used with polygons and polyhedra.
Usually 8 hours is a regular work-day.
it is usually attached to the transmision. You usually need to get to it from underneeth.
Power plants, being immobile usually, are usually found exactly where they were built.
A cuboid and a pyramid with a pentagonal base both have 6 faces. However, usually when this question is asked, the asker is looking for a regular solid for which all the faces are the same shape and size. In that case, only a cube qualifies.