15.I came across this old book while I＿＿my room.

• A、clean
• B、will clean
• C、have cleaned
• D、was cleaning

45.What can be seen in a rainforest according to the text?

• A、Leaves and branches of a tree never actually touch those of the other trees.
• B、Tree diseases make life more difficult for leaf-eating insects.
• C、Tall trees protect themselves from forest animals with their branches.
• D、The ground floor is all covered by leaves and branches.

54＿＿