Why is cloture very difficult to achieve?

Senators are famous for their debating prowess and would not easily give up to cloture.
The two-thirds vote of the Senate is almost impossible to attain.
Cloture can only be achieved by a three-fifths vote, and parties don’t usually have that kind of majority.
Senators usually wish to continue the discussion, and work hard to prevent members from voting for cloture.

According to the federal regulations, which of the following studies meets the definition of research with human subjects? a study of twenty 4th grade classrooms in which researchers ask the schools to systematically vary the time of day reading is taught, and collect weekly assessments of reading comprehension for each child over a three-month period.the collection of data, by a playground designer hired by the superintendent of schools, about the physical dimensions of school playgrounds, presence of fencing, and the kinds of equipment currently provided.a feasibility study for implementing a year-round school program, focusing on economic issues such a facilities utilization and transportation costs.an analysis of aggregate data comparing statewide high school graduation rates provided by the state department of public instruction, using county tax information.