Problem: On 12 March 1999, the Czech Republic, Hungary, and Poland joined NATO; Bulgaria, Estonia, Latvia, Lithuania, Romania, and Slovakia joined in March 2004; Albania joined on 1 April 2009.
In which year did Poland join NATO?
The answer is the following: 1999

Problem: iPod batteries are not designed to be removed or replaced by the user, although some users have been able to open the case themselves, usually following instructions from third-party vendors of iPod replacement batteries. Compounding the problem, Apple initially would not replace worn-out batteries. The official policy was that the customer should buy a refurbished replacement iPod, at a cost almost equivalent to a brand new one. All lithium-ion batteries lose capacity during their lifetime even when not in use (guidelines are available for prolonging life-span) and this situation led to a market for third-party battery replacement kits.
Whose directions can be followed to interact with iPod batteries?
The answer is the following: third-party vendors

Problem: Admissions are characterized as "most selective" by U.S. News & World Report. There were 35,099 applications for the undergraduate class of 2020 (entering 2016), and 3,751 (10.7%) were admitted, making Northwestern one of the most selective schools in the United States. For freshmen enrolling in the class of 2019, the interquartile range (middle 50%) on the SAT was 690–760 for critical reading and 710-800 for math, ACT composite scores for the middle 50% ranged from 31–34, and 91% ranked in the top ten percent of their high school class.
How selective are admissions at Northwestern characterized by U.S. News & World Report?
The answer is the following: most selective

Problem: Symptoms of mild zinc deficiency are diverse. Clinical outcomes include depressed growth, diarrhea, impotence and delayed sexual maturation, alopecia, eye and skin lesions, impaired appetite, altered cognition, impaired host defense properties, defects in carbohydrate utilization, and reproductive teratogenesis. Mild zinc deficiency depresses immunity, although excessive zinc does also. Animals with a diet deficient in zinc require twice as much food in order to attain the same weight gain as animals given sufficient zinc.
What is required for animals with zinc deficiency to gain the same weight as animals with sufficient zinc?
The answer is the following:
twice as much food