Oyster mushrooms typically get their nutrients from the damp logs on which they grow, but the fungi are also carnivorous,...

Let's begin by understanding the meaning of this sentence. We'll use our understanding of pause points and segment the sentence as shown - understanding and assimilating the meaning of each segment bit by bit!

Sentence Structure

• Oyster mushrooms typically get their nutrients
  • from the damp logs
    • on which they grow,
• but the fungi are also carnivorous,
  • with the ability to kill and consume microscopic worms
    • known as nematodes.

• As researcher Yen-Ping Hsueh has shown,
• the mushrooms release a toxin
  • that is deadly to nematodes
    • that [?] in contact with it.

Understanding the Meaning

The first sentence tells us about oyster mushrooms:

• They typically get nutrients from damp logs they grow on
• BUT they're also carnivorous
  • They can kill and consume tiny worms called nematodes

Now the second sentence explains HOW this works:

• 'As researcher Yen-Ping Hsueh has shown'
  • This cites the researcher who discovered this

• 'the mushrooms release a toxin'
  • So they have a toxin - a poison

This is where we have the blank. Let's look at the choices:

• They vary in whether the verb is singular or plural
  • has come (singular)
  • comes (singular)
  • is coming (singular)
  • come (plural)

To see what works here, let's read the rest of the sentence and understand what it's saying:

• 'that is deadly to nematodes that ______ in contact with it'

Now let's understand what this structure is telling us:

• The toxin is deadly to nematodes
  • But not just ANY nematodes
  • Specifically: nematodes that ______ in contact with it

• So we have: 'nematodes that ______'
  • This 'that' part is describing WHICH nematodes
  • The word 'that' refers back to 'nematodes'

What do we notice about the structure here?

• The verb in the blank needs to match 'nematodes'
  • 'Nematodes' is plural (more than one worm)
  • So we need a plural verb

• Looking at our choices, only one is plural: come

So we need: "nematodes that come in contact with it"

• This means: when nematodes come into contact with the toxin, it's deadly to them
• Simple present tense makes sense here - we're describing a general fact about what happens

GRAMMAR CONCEPT APPLIED

Subject-Verb Agreement with Relative Clauses

When you use "that" to add information about a noun (creating what's called a relative clause in grammar terms), the verb following "that" must agree in number with the noun it's referring back to:

Pattern:

• Plural noun + that + plural verb
• Singular noun + that + singular verb

Examples:

1. Plural: The students that study regularly perform better
   • "students" (plural) → "study" (plural)

1. Singular: The student that studies regularly performs better
   • "student" (singular) → "studies" (singular)

In this question:

• "nematodes that come in contact with it"
• "nematodes" (plural) → "come" (plural) ✓

Key tip: Even when there are other words in between, always identify what noun the "that" is referring back to, and match your verb to that noun's number.