阅读下面短文, 按照句子结构的语法性和上下文连贯的要求, 在空格处填入一个适当的词或使用括号中词语的正确形式填空。

    Sara and her father planned ____ trip to a mountain near their home. The path they chose____ (begin) at the foot of the mountain and led all the way ____ the top. Sara packed lunches earlier that morning. ____ (she) father filled their backpacks with other things and they  ____ (be) off!

    As they started up the path, Sara’s father pointed out many different____ (plant) that grew on the path. He showed Sara the ____ (different) between the____ (leaf) of trees.  Sara was glad ____ her father knew so much! She always learnt something whenever they went on a trip. This time, she was sure that she ____ learn more.

地球上既位于西半球、又属于东经度的范围是

依次填入下列各句中的虚词，恰当的一项是(　　)

①在激烈的市场竞争中一个勇于开拓的企业能获得荣誉当属不易，________，当前由于名目繁多的荣誉牌的泛滥，使其荣誉失去了应有的作用。

②不能把握到的我们必须泰然地放弃，________是诗，是自然，还是七彩斑斓的情意。

③我们学习，并不只是要积累别人创造出来的东西，我们________要提高自己的创造能力。

选词填空

兴奋   兴趣

①达尔文对稀奇古怪的昆虫很感____。

②父亲惊讶地看了一眼喜欢研究的儿子，____地举起那束报春花。

有下列四个命题：
①对于$\forall x\in R$,函数f(x)满足f(1+x)=f(1-x),则函数f(x)的最小正周期为2；
②所有指数函数的图象都经过点(0,1)；
③若实数a,b满足$a+b=1$,则$\frac{1}{a}+\frac{4}{b}$的最小值为9；
④已知两个非零向量$\overrightarrow{a}$,$\overrightarrow{b}$,则“$\overrightarrow{a}\perp \overrightarrow{b}$”是“$\overrightarrow{a}·\overrightarrow{b}=0$”的充要条件.
其中真命题的个数为(    )