题目

Even if they had to stop today, it would have been quite an accomplishment.But Brad Ryan and his 89-year-old grandmother Joy Ryan, who have _______ 29 national parks so far, have no intention of _______. The first one they saw was the Great Smoky Mountains National Park in 2015.Since then, he and Joy Ryan have seen many _______.“I remembered a(n) _______ conversation with my Grandma Joy when we’re _______ my 2009 Appalachian Trail hike from Georgia to Maine and she expressed _______ that she had never seen the mountains and _______ the great outdoors throughout her life, so I _______ her t如图所示，R1=R2＝R3＝R，电源内阻不计，电流表、电压表均理想。两表的示数分别为0．3A、2V，则电源电动势为______V，R=______Ω。若将两表的位置互换，则电压表示数为______V，电流表示数为______A。