单选题When does the speaker say that another significant change in instrument design took place?A In the early 19th century.B In the late 19th century.C In the early 20th century.D In the mid-20th century.

单选题

When does the speaker say that another significant change in instrument design took place?

In the early 19th century.

In the late 19th century.

In the early 20th century.

In the mid-20th century.

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