# 都变成大写
fruit = ["apple",'orange',"banana","balabala"]
print(fruit)
fruit = [x.upper() for x in fruit]
#挑选出以b开头的水果
b = []
for x in fruit:
if x.startswith("B"):
b.append(x)
print(b)
b = [x.lower() for x in fruit if x.startswith("B")]