As British scientist Peter Whibberley has observed, “the Earth is not a very good timekeeper.” Earth’s slightly irregular rotation rate means that measurements of time must be periodically adjusted. Specifically, an extra “leap second” (the 86,401st second of the day) is ______blank time based on the planet’s rotation lags a full nine-tenths of a second behind time kept by precise atomic clocks.

In 1637, the price of tulips skyrocketed in Amsterdam, with single bulbs of rare varieties selling for up to the equivalent of $200,000 in today’s US dollars. Some historians ______blank that this “tulip mania” was the first historical instance of an asset bubble, which occurs when investors drive prices to highs not supported by actual demand.

During the American Civil War, Thomas Morris Chester braved the front lines as a war correspondent for the Philadelphia Press. Amplifying the voices and experiences of Black soldiers ______blank of particular importance to Chester, who later became an activist and lawyer during the postwar Reconstruction period.

The haiku-like poems of Tomas Tranströmer, which present nature- and dream-influenced images in crisp, spare language, have earned the Swedish poet praise from leading contemporary ______blank them Nigerian American essayist and novelist Teju Cole, who has written that Tranströmer’s works “contain a luminous simplicity.”

In her book The Woman Warrior: Memoirs of a Girlhood Among Ghosts, author Maxine Hong Kingston examines themes ______blank childhood, womanhood, and Chinese American identity by intertwining autobiography and mythology.

Gathering accurate data on water flow in the United States is challenging because of the country’s millions of miles of ______blank the volume and speed of water at any given location can vary drastically over time.

A recent study tracked the number of bee species present in twenty-seven New York apple orchards over a ten-year period. ______blank found that when wild growth near an orchard was cleared, the number of different bee species visiting the orchard decreased. 

In 1903, environmentalist John Muir guided President Theodore Roosevelt on a scenic, sprawling trip through California’s Yosemite Valley. Upon returning from the three-day excursion, Roosevelt ______blank to conserve the nation’s wilderness areas, a vow he upheld for his remaining six years in office.

In 2018, a team of researchers led by Dr. Caitlin Whalen compiled every available measurement of ocean mixing rates from the past two decades. With this novel data set, the team was able to determine how current-driven mixing varies across ______blank and what impact it has on the distribution of heat and nutrients in the ocean.

To survive when water is scarce, embryos inside African turquoise killifish eggs ______blank a dormant state known as diapause. In this state, embryonic development is paused for as long as two years—longer than the life span of an adult killifish.

Formed in 1967 to foster political and economic stability within the Asia-Pacific region, the Association of Southeast Asian Nations was originally made up of five members: Thailand, the Philippines, Singapore, Malaysia, and Indonesia. By the end of the 1990s, the organization ______blank its initial membership.

Ten of William Shakespeare’s plays are classified as histories. Although each one of these plays, which include Henry V and Richard III, ______blank on a single historical figure (specifically, an English king), some, such as Henry VI Part One and Henry VI Part Two, feature different episodes from the same monarch’s life.     

To serve local families during the Great Depression, innovative New York City librarian Pura Belpré offered storytelling in both English and Spanish, an uncommon ______blank celebrated el Día de los Tres Reyes Magos, an important community holiday; and put on puppet shows dramatizing Puerto Rican folktales.

Cheng Dang and her colleagues at the University of Washington recently ran simulations to determine the extent to which individual snow ______blank affect the amount of light reflecting off a snowy surface.

The radiation that ______blank during the decay of radioactive atomic nuclei is known as gamma radiation.