They come 24 two sizes, and can expand in three places.
答案：(B) in
【句型】come in + 尺寸/顏色 字詞搭配「有……尺寸/顏色可供選擇」；by／from／down 都不合。
come 你最熟的是「來」，把它代進去讀成「它們來兩種尺寸」，怎麼讀都不通，於是你開始一個一個介系詞硬試。問題不在介系詞，在你沒認出這是一個整體用法：come in 後面接尺寸、顏色或款式時，意思是「有……可供選擇」（柯林斯英語詞典 Collins 的說法是：某類東西 come in 某個範圍的顏色、款式或尺寸，就表示它有那些選擇；劍橋詞典的例句是 The products come in three sizes.）。
把整句還原成白話：They come in two sizes, and can expand in three places.——這款鞋有兩種尺寸，而且可以在三個地方撐開。前面剛講完它的材質，這裡接著講它的規格，「有兩種尺寸可選」完全順著文意走。這個用法也可以掛在你早就會的招呼語上：Come in, please.（請進。）那個 come in 是「進來」，和這裡的「有……可供選擇」完全是兩回事——動詞加上介副詞之後，就要當成一個新的詞來記，不能把兩個字的意思相加。
by、from、down 都無法和 come 組成「有幾種尺寸」這個意思。要特別提醒的是 in 這個答案不能靠「翻譯」硬套，因為中文的「有兩種尺寸」裡根本沒有對應「在裡面」的字，這種題只能靠認出整組用法。
come in two sizes（有兩種尺寸）、come in all shapes and sizes（各種樣式都有、形形色色）、come in different colors（有不同顏色可選）、be available in（有……可供選擇）、be made of（由……製成，看得出原料）、similar to（與……相似）。
Shoes are hugely important for protecting our feet, especially in places like Africa, where healthcare provision is limited. Unfortunately, shoes are not always readily available for people living in poverty, 21 shoes that are the right size. Almost as soon as a child receives shoes to wear, he/she is likely to have grown out of them. Then the child has to 22 with shoes that are too small.
The Shoe That Grows, created by a charity called Because International, changes all this. It allows children to 23 their shoes' size as their feet grow. The innovative footwear resembles a common sandal and is made of leather straps and rubber soles, a material similar to that used in tires. They come 24 two sizes, and can expand in three places. The straps on the heel and toe control the length of the shoe, 25 the two on either side allow for different widths. With this special design, the shoes can "grow" up to five sizes and last for at least five years.