The Prime Minister was always cautious about leaving his redoubt in Belgrade.

Electricity is the most inefficient and costly way to heat a home. One kilowatt-hour of electricity creates about 3,400 British thermal units (BTUs). (BTUs are a standard heat measurement.) The price of electricity per kilowatt-hour is between $0.10 and $0.25 or between $29.35 and $73.13 per million BTUs.
In contrast, fuel oil, which produces 140,000 BTUs per gallon, costs about $8.33 to $13.89 per million BTUs. Natural gas, which produces 100,000 BTUs per therm, can be purchased for $5.00 to $22.50 per million BTUs. Oak firewood, which produces 26,000,000 BTUs per cord, costs $5.77 to $13.46 per million BTUs.
Choosing the right heating method for your home, based on the cost of fuel, may be more expensive at installation but will be cheaper in the long run.
According to the above passage, a BTU:

Determine which of the choices best solves the problem shown in the first picture and then mark the corresponding choice on your answer sheet. The problem is presented in the first drawing and the remaining four drawings are possible solutions.

For the valve shown in the figure above to open once each second, the cam must revolve at a rate of:

Which of the following isn't a type of telescope?