Four West Indian geckos, with human assistance, have recently entered the United States. The yellowheaded gecko, the ashy gecko, the reef gecko, and the ocellated gecko are presently inhabiting the tropical areas of the Keys and the tip of southern Florida. The Mediterranean gecko also arrived along the Gulf coast some time ago, via the West Indies. The only other geckos in the United States live in the Southwest. In extreme southern California, the leaf-gingered gecko lives in dry, rocky country and scampers over boulders at night, hiding by day in crevices. It has a slender, tapered tail and stalks insects by raising itself high on its legs, cocking its head, and twitching its tail nervously before leaping on its prey. In courtship, the tail is also waved by the male as he approaches the female.

Although most lizards are excellent climbers, the geckos are able to walk on smooth surfaces with the help of unique clinging devices under the toes. Also, the undersides of most geckos have pads of large scales, each of which bear microscopic hairs with hundreds of branches having minute, blunt ends that press against the surface that the gecko is on, enabling the gecko to cling to almost any surface. Like other lizards, geckos have the ability to shed their tails if attacked by an enemy. They stump heels and a new tail is grown in approximately the same shape as the original. Unlike most lizards, most geckos have no moveable eyelids. The nocturnal geckos have vertical pupils, which contract in bright light. All geckos, except several New Zealand species, lay eggs. The eggs have a tough, white shell and are laid under stones, behind window shutters or under bark.

Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions

In line 1, the author uses the words “human assistance” to mean ............

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