The speaker in "Birches compares the boy's climbing to (1 point)

O sweeping up broken glass.
filling a cup to the top.
O girls drying their hair,
O a forest full of spiderwebs.

O a forest full of spiderwebs.

The speaker in "Birches" compares the boy's climbing to a forest full of spiderwebs.

To determine the answer, let's break down the options provided and analyze them in relation to the poem "Birches" by Robert Frost.

1. "O sweeping up broken glass": This option does not align with the theme or imagery portrayed in the poem. There is no mention of broken glass or any related metaphor.

2. "filling a cup to the top": This option also does not directly connect to the poem's themes or imagery. The poem focuses on the act of climbing birch trees and the speaker's reflections on life.

3. "O girls drying their hair": This option is also not mentioned in the poem. It does not directly relate to the themes or actions described in "Birches."

4. "a forest full of spiderwebs": This option, however, aligns with the imagery and themes discussed in the poem. In "Birches," the speaker describes the birch tree trunks as being "like girls on hands and knees that throw their hair / Before them over their heads to dry in the sun." This simile draws a parallel between the boys climbing birch trees and the appearance of spiderwebs in a forest. The speaker compares the bending birch trees to the bending spiderwebs in the wind, emphasizing the sense of playfulness and temporary escape from the realities of life.

Therefore, the correct answer is: "O a forest full of spiderwebs."